Rhe CA]IADIA]I Mtileratoglsil JOUR]IIAIOF the MINERALOGICAT ASSOCIATIOIII OFGANADA

253

BUttETIItIDE I..ASSOCIATIOfII MINERATOGIOUE DUCATIIADA rHE CA]IADIA]I MTilERATOGlsil JOUR]IIAIOF THE MINERALOGICAT ASSOCIATIOIII OFGANADA

Volume31 June1993 Part2

Canadinn Mineralogist Vol. 31, pp. 253-296 (1993)

MINEHALS,MINERALOGV AND MINERALOGISTS: PAST,PRESENT AND FUTURE-

FRANKC. HAWTHORNE Depantnentof GeologicalSciences, University of Manitoba, Winnipeg,Manitoba R3T2N2

ABSTRACT

Minerals are the basicmaterials of the Earth, andvirtually everythingone doesin the Earth SciencesinvolveB minerals in one way or another,Minerals fumish a good part of the wealththat is the basisof our society,not just ascommercial products but as the soils that support our agriculture and the aquifers that hold our water supplies.Minerals have played a key role in the developmentof humanity.One of our first scientific actswas to distinguishbetween different mcks and minerals,and usethem as tools accordingto their properties.With the widespreaddevelopment of mining and trade,it becameimportant for peopleto recognizeminerals, and writings on mineral recognitionand propertieswere commonin many societies:China Greece,Rome, Persia.Arabia Italy, Germany. Extensivechemical work on mineralsbegan in the late 18thcentury, resulting in the developmentby Berzeliusofthe "anionic" classificationof minerals.The developmentof crystal-structure analysis hadamajoreffectonMineralogy;the workof W.L. Bragg gavean atomistic basis forourknowledgeof mineralchemistry andproperties, andthe workof V.M. Goldschmidtgave atheoretical 6asisfor thebehavior of elementsin geochemicalprocesses. The last 30 yearshas seen a flood of new techniquesinto Mineralogy: electron-microprobeanalysis and crystal-structurerefinement were followed by numerousspectroscopic techniques, many new microprobemethods for both elementaland isotopic analysis,and both scanningand transmissionelectron microscopy.The immenseamount of datastimulated the developmentof TheoreticalMineralogy. Atom ("ionic") andelectron('tovalent") models are now capableof accuratelycalculating stereochemical details and a wide array of physical and dynamicproperties. The first stepsto understandthe thermodynamicbasis of elementordering, elementexchange and mineral reactionshave now led to geothermobarometerscapable of determining equilibration conditions to l25oC and 11 kbar. Recent initiatives in surface mineralogyhave been encouraged by the importanceof surfaceproperties of mineralsin environmentalproblems. Mineralogy permeatesevery facet of Earth Sciences,and reachesout to many contiguousareas in Physics,Chemistry and Materials Science.Unforrunately, this great diversity has adverselyaffected the generalview ofMineralogy within the Earth Sciences:many Earth Scientistsare not conve$antwith the breadthand intellectual vitality of currentwork in Mineralogy.With pressureon University budgets,both from decreasingGovernment support and from the developmentof importantnew areas(e.8. ' EnvironmentalScienies), there is a dangerthatMineralogy will bediscarded as a specificcore discipline ofEarth Scienceresearch andteaching. If Mineralogy is taughthaphazardly as pa4s of the othersubdisciplines in Earth Sciences,students will not develop a feel for thl divenity of mineralsand their behaviorin the wide variety of tenestrial environments.The end result will be a generationof Earth Scientistswho lack fundamentalundentanding of the materialswith which they work, and who will be incapableof adaptingto new areasof expansionwithin andperipheral to Earth Sciences.It is up to Mineralogiststo preventthis from happening.

Keyword Mineralogy.

' Presidentialaddress delivered at Wolfville, Nova Scotiaon May 26th,1992. 254 THE CANADIAN MINERALOGIST

SOMMAIRE

Les min6rauxconstituent les mat6riauxde basede la terre; d'une fagon ou d'une autre,les activit6sde tout g6oscienufique gravitentautour des min6raux. Ce sont les min6rauxqui foumissentune partie imporrantede la richessequ'est le fondementde none soci6t6,non seulementsous la guisede produitscommerciaux, mais aussi comme constituents des sols qui supportentnotre agricultureet des couchesaquifbres qui contiennentles ressourcesd'eau souterraine.lrs min6rauxontjou6 un r6le-cl6 dansle ddveloppementde I'humanit6. Un despremiers gestes scientifiques a 6t6la discriminationparmi lesdiffdrentes roches et mindraux, afin demieux choisirles mat6riauxpropices d la fabricationd'outils. Avec le d6veloppementde I'industrie minidreet des&hanges commerciales,il s'est avdrdimportant de reconnaltreles mindraux.Aussi, les &rits sur les caractdristiqueset les propri6t€sdes min6rauxont-ils 6td courann dansplusieurs socidtds, en Chine,en Grdce,en Perse,en Arabie, en Italie et en Allemagne,d titre d'exemples. L'6tude de la chimie desmin6raux a d6butdvers la fin du dix-huitidmesidcle; de telles 6tudesont men6au d6veloppmentde la classification"anionique" desmindraux par Berzelius.Ia possibilitdde d6terminerla structurecristalline desmin6raux a eu un effet majeur sur la Min6ralogie.Les travauxde W.L. Bragg ont donndune baseatomiste i nos connaissancesde la composition chimique et des propri6t6sdes rnin6raux.Les travaux de V.M. Goldschmidtont foumi la baseth6orique du comportementdes 6l6mentsdans les processus g6ochimiques.I-a demibre trentaine d'ann&s a vu uneflopp6edetechniques nouvelles enMin6ralogie: la possibilit6d'effectuer des analyses h la microsondedlectronique de mindrauxet d'en affiner la structurecristalline a 6td suivie par de nombreusestechniques spectroscopiques, avec plusieurs m6thodes nouvelles d'analyses par microsondepour ddterminer soit la teneurdes 6l6ments ou les rapportsisotopiques, et la microscopiedlectronique i balayageet par transmission.La quantit6 immensede donn6esnouvelles a stimul6 le d6veloppementde la Mindralogiethdorique. Des modblesatoniques ('toniques") et 6lectroniques('tovalents") sont maintenantcapables de calculerles ddtailsst6r6ochimiques et un 6ventailimposant de propridt6s physiqueset dynamiques.Les premibres6bauches d'une comprdhensionde la basethermodynamique de la mise en ordre des 6l6ments,de leur 6change,et des rdactionsparmi ces mindrauxont permis de formuler des g6othermobaromdtrescapables de ddterminerles conditions d'6quilibre A25'C et i I kilobar prbs.Des initiatives r6centes dans l'6tude dessurfaces ont 6tdentreprises i causede la grandeimportance des propri6t6s des surfaces dans les problbmesde l'environnement. l,a Min6ralogieinfluence profond6ment chaque aspect des sciences de la terre,et elle 6tablit desliens avec les domainescontigus en physique,chimie, et sciencedes matdriaux.Malheureusement, cette grande divenit6 a exerc6un effet n6gatif dansl'opinion qu'ont plusieun i propos du rdle de la Mn6ralogie dansles sciencesde la terre. Plusieursg6oscientifiques ne sont pas bien renseigndsi propos de I'envergureet de la vitalit6 intellectuelledes travaux courantsen Min6ralogie.Avec les compressions budg6tairesdans nos universitds,d caused'une diminurion dansles octrois gouvenementauxet du ddveloppementde domaines nouveaux,comme par exempleles sciencesde l'environnement,je pergoisun dangerque la Min6ralogiesera ray6e de la liste des disciplinesessentielles dans l'enseignement et la rechercheen sciencesde la terre.Si on enseignela mindralogiede fagonal6atoile commepartie d'autressous-disciplines dans les sciencesde la terre, commentles dtudiantspourront-ils apprendre i proposde la diversit6des mindraux et leur comportementdans une varidt6 de milieux terrestres?11 en rdsulterai! 6ventuellement,une g€neration deg6oscientifiques qui nepossddentpasune maltrise des matfriaux qu'ils 6tudient,etqui sontincapablesde s'adapteraux nouvelles disciplinesau sein des sciencesde la tene et dansles domainespluridisciplinaires connexes. Il incombeaux min6ralogistesde faire les ddmarchesn6cessaires porr contr€rcette 6volution n6faste.

Clraduit par la Rddaction)

M ots- c 16: Mindralogie.

Ir\'rRoDUc"noN TITE CENTR,AL RoLEoF MINERALOGY INTI{E EARTTTSCTENCES Many yearsago, I was an undergraduatein Geology attheRoyal School ofMines in London.Irememberthaf The centralrole of Mineralogy in the Earth Sciences minerals and their recognition were emphasizedfrom is illustratedschematically in Figure 1. There are many the start of the undergraduateprograrl and this contin- more branchesof the Earth Sciencesthat could be ued throughto the end.The messagewas simple: r/yoa included(e.9., geochemistry, paleontology, geochronol- can't recognizeminerals, you won'tfind mines!Miner- ogy), and toward the end of this article, I will mention alogy was emphasizedas one of the core disciplinesof the role of Mneralogy in some of the less traditional Geology, what today is more fashionableto call Geo- areasof the Earth Sciences(e.9., EnvironmentalSci- logical Sciences.It hasalways been surprising to methat ences,Atmospheric Sciences). However, the subsetof Mineralogy receivesmuch less attention in the Earth topics in Figure I is sufficient to make the point that Sciencescurriculaof North America.asrninerals are the virtually everyttring one does in the Earttr Sciences basic materialsof the Eanh (andplanets), and furnish a involves mineralsin one way or another. goodproportion ofthe wealththat supportsour society. In Petrology,be it igneous,sedimentary or metamor- MINERAIJ. MINERALOGY AND MINERALOGISTS 255

exploitation,but againMineralogy has its partto play in designingoptimum processesof ore beneficiationand extraction. tn Geophysics,one is concernedwith the physicalproperties ofminerals. The elasticproperties of minerals are of interest to the seismologist,and the magnetic properties of minerals are of interest to the paleomagicians;this parallelism of interests is CHEMICAI. apparent in the current cooperative effort of SEDIMENTOLOGY geophysicistsand mineral physicistson studiesof the Earth'smantle and core. In PhysicalSedimentology, the Ftc. l. The central role of Mineralogy in the Earth Sciences. behavior of minerals is governedto a large extent by &eir physical properties.In ChemicalSedimentology, the dissolution and crystallizationof soluble minerals areof primary interest;details of chemicalcomposition, zoning, crystal morphology and habit, parageneticse- quence and relative stability fall directly within the realms of Sedimentologyand Minetalogy. In many phic, one looks at the minerals in the rocks. The aspectsof StructuralGeology, one is coicernedwith the petrologist determinesthe major- and trace-element physical (and chemical) properties of minerals; such compositionsof the minerals,either directly by electrdn-, contrasting characteristicsas brittle deformation and ion- and PD(E-microprobeanalysis, or indirectly by creep can vary radically from one mineral to another, petrographicmethods, cathodoluminescence or epifluo' and canbe very anisotropicwithin single minerals.The rescencemicroscopy; chemical zoning is characterized, relationshipbetween structure and properties,and the and both stable-and radiogenic-isotopiccharacteristics way in which thesechanges with pressureand tempera- are measured.Physical parameters such as grain shape, ture, fall both within StructuralGeology and Mineral- roughnessand fractal dimensionsof grain boundaries ogy. are measured.Nearly all of these characteristicsare Thus Mineralogy is a core discipline within Earth propertiesof minerals,and the intrinsic structureof the Sciences;the moreone knows about minerals, the better minerals constrainstheir variationjust as the petroge- Earth Scientist one will be, no matter what one's netic conditionspromote their variation.Without under- individual specialization. standing the relative roles of these two factors in influencing mineral composition, we constrain our- MINERALS N.I PREHISTOPJCTINGS selvesto imperfect models of petrogeneticprocesses. Likewise, the role of fluids within rocks hingeson the It is no accident that we date the prehistory of detailsof the surfacestructure and chemistry of minerals humanityby the materialswith which our predecessors (possibly moderatedby biofllm activity in many envi made their tools. Tools are one of the more enduring ronments),and if we are ever to developmechanistic creationsof prehistoric humanity, and they document models of fluid-rock interactions,a knowledgeof the surfacestucture andproperties ofminerals is essential. Note that we havediscussed Petrology as a singletopic ratherthandividing it up into its traditionalsubdivisions. Historically, therewas often a tendencyfor a mineralo- gist to be associatedwith onespecific area ofPetrology, to the ultimate detrimentof Mineralogy as a separate discipline.Mineralogists are interestedin mineralsand their behavior,and this interestthus pervadesall areas of Eanh Sciences.There is nothingto stopa mineralogist being simultaneouslyinterested in the properties of (Mg,Fe)SiO3perovskite, the dolomite problem,and the staurolite problem; such a catholic range of interests would be consideredbizarre in a petrologisl but sucha wide rangeof interestson the part of a mineralogistcan leadto importantcross-fertilization between suMiscipli nes. In Economic(or ore deposits)Geology, one looks at both ore and gangueminerals with the methodsand scientific motivation of fte petrologist.Additional fac- tors comeinto play in termsof resourceevaluation and Frc. 2. Stone-age artifacts of flint and obsidian. 256 T1IE CANADIAN MINERALOGIST

Ftc.3a. Naturally occurring native copper.

increasingtechnological sophistication. One of our first of theNeolithic period,approximately 40 differentrocks scientificact$ was to distinguishbetween different rocks and mineralswere in commonuse. and minerals,and use them as tools accordingto their properties. Metals and the BronzeAge

andthe StoneAge The first metals to be used were the naturally occurring native metals (Fig. 3). These were greafly Our earlyancestors were vegetarians. With theadvent sought after by Stone Age humanity, but for their of CromagnonMan and Woman,our ancestorsbecame curiosity andornamental value rather than for tool-mak- omnivorous(with the additionof meatto their diet). The ing. The naturalmetals are all too soft for tools,but could useoftools was an essentialadjunct to this change,and be cold-worked into ornamentsand jewelry. Iron, in spearpoints, knives and scraperswere developed.The particular,was greatly prized for its rarity, asit wasonly suitability of certain materialsfor thesepurposes wts known ftom meteorites- the ooHeavenlyMetal" of the realized very rapidly, and obsidian and flint became Sumerians. widely used@ig. 2). As humanitybegan to work natural Around this time, someonediscovered that heating materials,further advancesbecame inevitable. One can metalsgreatly promotes the easewith which they canbe picture a skin-clad troglodite on the chalk downs of worked.It is probablethat this discoverysoon gave rise England(perhaps an ancestorofRogerMirchell) picking to the technique of smelting, whereby a mixture of up a heavy pyrite nodule to break a flint into smaller copperores gave native copper on heating.This is almost more workable pieces; fue was widely started by certainly the origin of the discoveryof bronze;heavy striking pyrite with flint. Naturally occurring poisons metallic or semimetallicminerals were heated to extract suchas arsenicwere known and used.Toward the end the "copper", but in fact gavebronze. Early bronzewas MINERALS. MINERALOGY AND MINERALOGISTS 257

Frc. 3b. Naturally occuning native gold.

a mixtureof copperand arsenic, derived from domeykite TheIron Age or algodonite.However, it wassoon found thata mixture of cassiteriteand copperore yielded betterbronze, and About 1400B.C. saw the start of the Iron Age. This this was the basis of the bronze-agetechnology that heraldeda major changein humansociety, as iton ores developedthroughout Europe and Asia. arevery cornmon,and iron forms very hardand durable 258 THE CANADIAN MINERALOGIST

Ftc.3c. Naturally occurring native silver. tools. In addition, the technologyof smelting and working iron is much more complexthan that required for the variousalloys of copper,and different ores of iron must be treatedin different ways.As a consequenceof this, it becameimportant that a large numberof people be able to recognizethe different typesof iron ore, and it is perhapsnot a coincidencethat the earliestwritings on mineralsdate from the early Iron Age.

Nonmetallicminerals

ThroughouttheStone, Bronze and Iron Ages,human- ity also beganto use an increasingnumber of minerals unrelatedto the manufactureof tools. Fascinationwith Art seemsan intrinsic property of the humanpsyche, a statementthat seemsas true for our ancestorsas it does for ustoday. Cave art is ourearliest record ofhumanity,s

TABLEI. EARLI URIT]NGSOI{ I'IINERALS -1100B.c. Indla Y&as -700B.c. China Compllatlonsof mlnerals -300B.c. India Dsscrlptionsof nlnerals 384-322B.C. Greoce Arlstotle - lteterologlca 370-287B.C. Greece Thoophrastus- 0n Stores 23-79A.D. Rom€ Pliny - ,trslorta Naturalls 8th century Parsla ilablr lbn Hayyan 9th century Arabla Al Khlndl 980-1037A.D. Persia Avlcennalbn Slna 15404.0. Italy Blrlngucclo- Plrotecnla (370-287 1556A.D. eornany Agrlcola - DeRe l'letalllca FIc. 4. Theophrastus B.C.), authorof "History of Stones". MINERAI-S. MINERALOGY AND MINERALOGISTS 259

Frc. 3d. Naturally occurringnative iron.

artistic spirit. Its first expressionis asrough scratchings from the seventh century B.C., and further Indian on cave walls, possibly of religious or superstitious manuscripts from the third century B.C. The first origin. However, this soon changed,and colored pig- Europeanwork datesfrom this time: Aristotle (384-322 ments becamecommon: manganeseoxides for black, B.C.) wrote briefly on minerals inhis Meteorologica. hematitefor red, malachitefor gteen. However,the first scientific work on (asdistinct from a It alsoseems a characteristicfeature ofhuman beings simple listing of) minerals is due to Theophrastus o'caves" to adorn themselvesand their with beautiful (370-287B.C.). Theopbrastus(Ftg. 4) was a pupil of objects.Ornaments of amethyst,turquoise, jade, mala- Aristotle, andsucceeded him asthe headofthe Lyceum chite,garnet, gold andsilver werewidespread, and trade in Athens; he wrote the first mineralogy text, the in preciousstones was extensive.In addition,the firing "History of Stones", thought to be his lecture notes. of clay to make poftery was an important advancein Theophrastusclassified minerals according to strict humansociety, and the drive to produceaesthetic objects Aristotelian principles, basing his work firmly on the led to the developmentof glazing and the manufacture physical properties of minerals, and eschewingany of glass. magical or fabled medicinal overtonesthat were so Thus the early developmentof humanity is intrinsi- characteristicof many later compilations. cally associatedwith therecognition and use of minerals. Pliny (Gaius Plinius Secundius,the Eldet' 23-:79 As the hon Age began,there was exiensivetrade in a A.D.), the celebratedRoman encyclopedist, produced a wide variety of minerals,and the ability to recognize 37-volume work:.Historia Naturalis (there may have mineralsand be familiar with their propertiesand uses beenmore volumes "in the pipeline",but volcanologists - becameof importanceto an increasinglylarge number will recognizethe dateof Pliny's death he was killed of people. at Pompeiiby theeruption of Vesuvius).Five of Pliny's volumesdeal with minerals,gemstones and their treat- EARLY WRMNGS ON MINERALS ment. It is perhapsa reflection on human nature that Pliny goesinto detail on the many gemstone-enhance- The requirement that more and more people be menttechniques current at that time: oiling' dyeing,the propertiesled to the useof backingfoils, and the manufactureof composite conversantwith mineralsand their oo...there fint writings on minerals(Table 1). The earliestknown stones.He writes: aredescriptions as to how to liierature is the Indian Vedasthat datefrom about I 100 give the colour of sm.aragdas(emerald) to crystallus B.C. Thereare Chinese compilations of mineralsdating (rock crystal) and how to initiate other transparent 260 T}IE CANADIAN MINERALOGIST

CEORGII AGRICOLAE DE RE METALLICA LIBRI XIT> QVIT bu O6q lnFnrmq }Lchrne,x m drnrq rl .\itirtiu sr fpc{ruu.ammodolu

Ftc.5. IllusftationsfromDeRe Metallicaby CterirypusAgricc la; left: frontispiece;right: mining in the fifteenth century.

BASILEAE M' D> LVt>

Co Eiail4io lmpnrrcirbed r. 6( Gilrio R.B{ d S..F.--

gems...To tell thetruth he mustbea scientistl,there is minerals. The next work to take a more scientific no fraud or deceitin the world which yields greatergain approachis that of the eight-centuryPersian scientist and profit than that of counterfeitinggems". Jabir Ibn Hayyan. He summarizedhis philosophy as Detailedrecipes for gemstoneenhancement are given follows: "The first essentialis that thou shouldst do inthe Papyrus GraecusHolmiensis, transcribed about experiments;philosophers delight in the excellenceof 400 A.D. in Egypt "Forthepreparationof emerald:mix their experimentalmethods", and followed this up by together in a small jw lD drachmaof copper green classiffing mineralsaccording to their externalappear- (verdigris), l/2 drachmaof Armenian blue (chryso- anceand physical properties. Such schemes were further colla),1/2 cup ofthe urineof anuncorupted youth, and developedby the Arab philosopherAl Kindi and the A3 the fluid of a steer'sgall. Put into this the stones, Persianalchemists Ar Razi and Avicenna.Throughout about24 piecesweighing about 1/2 oboluseach. Put the the Pre-Renaissanceperiod, the number of known lid on thejar, sealthe lid all aroundwith clay, and heat mineralsincreased rapidly, and the phenomenological for six hours over a gentle fire madeof olive-wood.... approachtaken by the morerigorous ofthe philosophers You will find that they havebecome emeralds." was essentialto the developmentof Mineralogy as a In 97 A.D., the Chineseambassador to Antioch. the u$efulscience. capital of Roman Syria, included in his report back to China the following: "The articles made of rare and THE RENAISSANCE AND BTyoNn precious stones produced in this country are sham curiosities,and mostly not genuineo'.Things apparently The Renaissancewas accompanied by a greatexpan- becameso bad that in -300 A.D., the EmperorDio- sion in economicactivity throughoutEurope. In particu- cletian orderedall books describingthe fabrication of lar, extensive mining and smelting works arose in artificial gernstonesto be burned. For those further Germanyat thebeginning of thesixteenth century. It was interestedin this fascinatingtopic, the book by Nassau here that GeorgeBauer latinized his nameto Georgius (1983)is recommended. Agricola, and published his celebratedwork De Re Many subsequentwdtings commonlyrailed to differ- Metallica. This work comprehensivelydocuments in entiatebetween fact and fantasy,and the onset of the 'DarkAges" detail all aspectsof mineralsand mining, and describes in Europesaw a much-reduceddemand for the metallurgicaltechniques in useat that time (Fig. 5). MINERAIJ. MINERALOGY AND MINERALOGISTS 26'.|

TABLE2. tltPoRTA!{TEARTY ADVAIICES ltl IllE Plltslcs 0F l'lINEMls

Lucretlus 99-55 B.C. AtoElq hypothqsls ,r. Koppl6r 16ll A.lL SJ@try of snorflokes clos*packlng of 'ato!s' N. Stono t669 A.D. stono's hypothesls, constanct of intorfaclal anglgs ln qusrtz A. lemor t750-1817A.D. Last grea! physlcal cl8ssiflcation of Elneral s L. Ron6dE I'lsle 1736-1790A.D. Lo{ of constrncy of lnlEffaclal Nnglos 'unlt t*q R.-J. Hauy 1743-1922A.D. Idoas on cgll' and translatlonal sy@iry C. let3s 1815A.D. Crystal lographtc ues, sy@try ax03 t. llohs 18254.0. nohs hardniss scale ,1. Hossel lgl0 A.D. Derlyatlon of ths 32 crystal classes A. Bravals 18{g A.D. Derlvatlon of tho l4 spacelattlces E.S. F€dErov Fffi-ll&",1 of the 230 spaco groups; 0Erlvrtlon A. Schoenfllos 1880-1890A.0. close packlng, proposedcrYstal I'wi@l I. Barlw structlro of hallte

directionalin nature,crystal habit dependingon relative ratesof growth in different directions. Steno'shypothesis was a very importantadvance, as Frc. 6. The formation of snow crystals vla close-packingof it establishedCrystallography as a quantitativescience, "snowatoms"; after Keppler in 161I . and external form becameof great importancein the ensuing classificationsand descriptionsof minerals. These reachedtheir zenith in the work of Abraham Werner (1750-1817),professor of Mineralogyf at Freiburg, Germany,who developeda comprehensive Agricola formally definedthe mineral properties that we schemeof classificationfor -300 minerals, that was are familiar with today: color, transparency,luster, importantfor the standardizationof mineraldescriptions hardness,cleavage and flexibility. He usedthis as the andmineral nomenclature.As an aside,Werner was the basisfor a classificationof mineralsbased on physical fint to introducethe custom of naming mineralsafter properties.In from his own observationshe addition, specific people (Mitchell 1979): prehnite (after Col. proposedthat the formation of vein mineralsis a result Hendrik von hehn), torbernite (after Torben D. of circulating undergroundfluids. Approximatelycon- Bergman,a prominent Swedishmineralogist and ana- with Agricola was VannoccioBiringuc- temporaneous lyst) and witherite (after William Withering). Although cio of Siena Italy. In his work on metallurgy,Pirotecnia, this createdconsiderable controversy at the time (and which appearedin 1540, he developed a physical has done so ever since), it has proven too popular a classificationof minerals. similar in scopeto that of customfor its opponents.Although Werner'sclassifica- Agricola. tion was very importantat the time, the developmentof chemicalmineralogy had alreadybegun, signalling the mineral Thephysics ofminerals end of physical properties as the basis for classification. Developmentsin Crystallographyproceeded apace Lucretius(99-55 B.C.) hadlrstproposed that matter Clable2). Following the developmentof the goniometer (he explicitly included minerals)consisted of atomsof by Carangeotin 1780, Jean Baptiste Louis Rom6 de tfie "elements"earth, air, fire and water.However, this I'Isle (173G1790)confirmed Steno's hypothesis, estab- was essentially an axiomatic proposition. The lrst lishing the law of constancy of interfacial angles. inductive work on the internal constitutionof minerals However,the major advanceof this periodwas made by is attributedto JohannesKeppler. In 1611,he gavethe Ren6-JustHany Q743-1822). In tus Traitd de cristal- first descriptionof the hexagonalsymmetry of snow- lographie, published n 1784, Haiiy proposed that flakes, proposedthat they are composedof a planar crystalsconsist of identical inte$al moleculesstacked close-packedanangement of spherical'oatoms" of ice together,and showed how differentmodifications of the Gig. 6), andrecognized the uniquenafire of both cubic samestacking could give rise to different crystal forms andhexagonal close-packed arrangements ofspheres. In 1669,Nicolaus Steno (the Dane, Niels Stensen) showed that the interfacialangles of quartzcrystals are constant, irrespective of crystal habit; he also proposed that *It is worth noting that Mineralogy was the fint of the crystals grow by the adhesionof particles from an Geological Sciencesto be sufficiently well establishedand external fluid, and concluded that crystal growth is useful to be taughtat University. 262 TTIECANADIAN MINERALOGIST

Fto. 7. Different crystal forms derived from the stacking of identical "blocks"; after Rend-JustHa0y, l7 43-1822.

of the samematerial (Fig. 7). The similarity of his ideas crystal-structurearrangement of halite; however, this to those of the unit cell and the spacelattice is very was largely ignored by the scienceof the day, and striking.In 1815,Christian Weiss followed this up by vindication of his views had to await the technologyof developingthe idea of crystallographicaxes and their the twentiethcentury. relationshipto symmetryaxes; he recognizedthe cubic, tetragonal,orthorhombic, hexagonal and trigonal sys- The chzm.istryof minerals tems.In 1825.Friedrich Mohs. inventorof the Mohs hardnessscale" discovered the monoclinic and triclinic Abraham Werner's great classificationof minerals crystalsystems, and in 1830,Johann Hessel derived the was tlte last gasp of physical propertiesas a basis for 32 crystalclasses. Auguste Bravais derived the 14space mineral classification.The work of the more systematic latticesin 1848,and the classical age of crystallography alchemists(Fig. 8) eventuallybegan to bear fruit with came to a close with the derivation of the 230 space the gradual developmentof chemical mineralogy. In groupsby E.S.Fedorov, Artur Schoenfliesand Wiltam 1758, Kronstedtdeveloped a classificationof minerals Barlow. Barlow also took the first steostoward a more that was a hybrid of chemicaland physical criteria, and fundamentalunderstanding of minerali by proposingthe the chemical study of minerals began to accelerate, MINERALS, MINERALOGY AND MINERALOGISTS 263

THE SYSTEM OF new elements,established the chemicalbasis of Miner- alogy andthe pre-eminenceofBerzelius and his idea. The year 1837 is a landmark in the history of MINERALOGY Mineralogy.It marksthe dateof publicationof the fust edition of A Systemof Mineralogy by JamesDwight of lames Dwight Dann and Muard. Salisbury Datw Dana (1813-1895).The fourth edition of this work Yale Unioersitr, 1837 - 1892 appearedin 1854,and in this edition, Dana introduced the "modern" chemical classificationscheme of Ber- zelius, and systematically applied it to all known SEYENTIIEDITION minerals.Dw:a's Systemremains the only all-encom- &dtdy Foriuen anil Cratly Enlargd passingmineral classification,and is still in use today By (Frg.8). CIIARLES PALACIIE I shouldperhaps say somethingabout the emphasis on mineral classificationthat pervadesthe above ac- tic lotc IIARRY BEIiMAN count of the history of Mineralogy.Many scientistsfeel azd CLIFFORD FITONDEL that mattersofclassification are trivial, andbelong to the Horaard Uniaersity realm of "stamp collecting" rather than "real science"; all this shows is that these people are so narrowly Ftc. 8. Frontispiece of the seventh edition of The System of focused that they lack the need to organize their Mineralogy of James Doyle and Edward Salisbury Dana knowledge.A scientfficclassificarton is a disrtilationof GaJacheet al.1944). our lcnowledgeconceming the nature of the objects underconsideration. The morefundamental our knowl- edge,the "deeper"and more effective the classification; perhapsthe best exampleof this is the periodic table of the elements.However, it still needsto be emphasized particularly with the systematicstudies and writings of thatthe "discovery"of atomsandthe development ofthe suchscientists as TorbernBergman (1735-1784). Many periodic table were accomplishmentsof the "stamp famous classical chemical mineralogists* carried out collectors" and &e classifiers. and not the result of analytical studiesof the mineralsknown at that time. "more fundamental"discoveries at a later date.We can Numerousnew mineralsand twenty-five new chemical take the stateof mineral classificationas a long-term elementswere discoveredbetween 1790 and 1830.a indicatorof our fundamentalknowledge of Mineralogy: periodof amazinggrowth in scientificknowledge. Akey frst, the developmentof a physical classification,then factor here was the discovery' of the laws of the developmentof a chemicalclassification and, in this stoichiometry by the English chemist John Dalton century,the beginningsof a structuralclassification of (1766-1844).With thedevelopment of Dalton'satomic minerals.' theory, the importanceof the chemicalconstitution of mineralswas soon realized,and all seriousschemes of CENTURY mineral classification subsequentlyhad their basis in THBTwsMrsrH mineral chemistry. In this period,one figure standsout abovethe others: The twentieth century has seena revolution in the JonJacob Berzelius ( 1779-1848).This famous Swedish basic structureof Science.In 1895, J.J. Thompson mineralogist-+hemistdeveloped a mineralclassifi cation (Cavendishhofessor of Physics)remarked that Physics based on the elechonegativeelements, giving such classesof minerals as oxides, halides,phosphates, sulfatesand silicates, essentially the schemethat we still usetoday. At this time, FrangoisBeudant and William H. Wollaston (who said that naming minerals after TABLE3. EARLYCHB.IICAL I.IINERALOGISTS ND fiEIR people is not a good idea!) discoveredthe conceptof OFFSPRING solid solution in minerals. and Eilhardt Mitscherlich Kronstodt L722-1765 Cronstedtite (1794-1863)proposed the idea of polymorphism.The Bergoan 1735-U84 Torbsrnlto suddensuccess in bringing orderto a rapidly increasing B€rzelius 1779-1848 Berzeli lte numberof minerals,to saynothing of discoveringmany Vauquelln 1763-1820 VauquelI nlte cadolln 1760-1852 cadollnl to Tennant l76t-18t7 Tennanlte l aston 1766-1826 !ollastonlte *Most l{ol of the well-known chemical mineralogistshave their Stroneyor 1778-1&15 Stroneyerlte mineral (Table whereas physical 3), of the mineralogistsand Arfvodson 1792-184t Arfvedsonlte crystallographers,only one, Rend-JustHaiiy (hauyne),is so Rose 1795-1864 Rossllte commemorated. 2U HE CANADIAN MINERALOGIST

The Structut"eoJ' Som,eCrystal.s cts fnd,icq,tecl by tlrcir Difri'ccctiori o1fX-rays. By W. L Bnecc,B.A

(Communicatodby Prof. \Y. E. Bragg, F.ILS. ReceivedJune 2l,-Read June26, 1913.)

[Pr.rtr lO.]

A tterr'trtctltcrtl of inlesiigal,ing the stmcirrre of t crystrrl lns lt.crr :rllirrrlt'rl Ity tlte trolk of frrutr* lnrl his collr'lxlrtots <-rntlre dilt'rrrctirnrof X-ritls lr.v 'l'!ur ct'r'rfirls. l,lrtrnoruerrtrvltich tLer. rvcre tle lirst l.o irrvt.stig:rte,irtrrl lllritil llrvc sirtce lreett oltseltctl l-n'trrlny otlrcls, lcrul tlrerlsellcs n'rulil.r't,r thc cxlrlrtrrrttiott1r1ry1x;!igd l.y Irure, rvlur sullxrscrltlrlt clcctrorurlgneticsrr\.(,s of velr- sltor'l rvtve-lengths rvete tlitrructatl lry rr scl r,f srrrrrll olrslirr:L:s art'rtngedorr t rrgul:rr lxrirrl ststelr irr sltrce. fn alulysirrg tlrc irrtcrfrrtrrc(' 1)attenl uirtrrirrerlrvitL rt zincl,lerulecr;'stal, Inrc, irr lris rq.igi111lrrrr,rrrrrir., c&llle tr) tlro trnrciusion l,lurt the yn.irrruryratliatiun l)osfti$srrll sl'c(.tl.ulu cotrsistirrgof rrrrl'r'orr')rirnrls', irr flcb, [hal it rvirgcotul,oserl of t so.icsrrl' si\ r,r selen rl lrrrrxirnalely l urtuogeneorrsrrale ttaius.

Ftc.9. The beginningof W.L. Bragg'shistonc paperon the structureof crystals;afterBragg (1913).

ATOMIC STRT]CTURE OF MINERALS

BY \xr. L, BRA@ larguoilb, Ptolesor ol Pbyitt in Tbe Y;ct6)4 Unirdtitt ol ilacbeta

FIc. 10. left: W.L. Bmgg; righc frontispieceof TheAtomic Strucnre of Minzrals @rlagg1937). MINERALS. MINERALOGY AND MINERALOGISTS 255

TSE PRTNCIPIES DETERMINITYG TgE STRUCTT]RI OF COMPLEX IONIC CRTSAALS

B! LM PA@NC [email protected] I'@l}@5.t9S l. Th3 Reladve Stability of Altetlatlve Structut€s of loltc Crysta!&- The elqcidatioq ol tle factc tletemining tle relatire stabilitv of altet- natirc qystalliue strrcfir6 of a sbstee eould be of the gBtst siglifr- mc in tle delrlopEst of the thct of the slid state. $ay, fc s- mple, do sme of tle alkali halidc cysta[ize wit! tle sodim chloricle structure @d roe wit! the sim cbloride structure? Slry de ti taim dicide sds difi@t mditiom me tle difr@t structrc of rutile, b@kite dd @te? Wly alc alminu iuciliete, Al:SiOr Fr, qystallize wit! tle structre of toPs ud not rit! erc oths sttuc- tre? Tbs quetioc m mered fomally b'y the statmot thrt itr each cas the structue with the midmum fre eucgy is stabb. fhis aws, howerq, is not utidyiag; what is deired i! ffi atomistic md qumtum tlmtical m is the esplauatim of this miaimm frc uergy h tms of at(m or i@ od tleir propertia.

FI6. 11. left: Linus Pauling; right: the beginning of Linus Pauling'sclassic paper on "Pauling's rules" (Pauling 1929).

was nearly a "finished" science; two small matters of NaCl anangedin somefashion; W.L. Bragg (Fig. 9) remainedto be solved.and Sciencewould becomethe showedthat Barlow wasright andthat the conventional straightforwardapplication ofphysical laws. One never view waswrong. The elegance ofBragg's conception is ceasesto be amazedat such a lack of appreciationfor amazing.Normally, an experimentinvolves one \n- thecomplexity of Nature;the search for "universallaws" known andone or moreknown quantitiesor facts;in this often seemsto blind peopleto the possibility that their particularcase, there were two unknowns:(i) whetherX 'lrniversal" laws may only be applicable (or perhaps rayshave a wave-likebehavior; (ii) whethercrystals are 'televant") within a specific domain of conditions. periodic.Bragg's interpretationshowed both of theseto Anyway, the'two smallmatters" referred to abovegave betrueand, as abonus,produced the fust experimentally rise to quantumtheory and relativity, andrevolutionized determinedatomic arangement of a crystal. our practice and understandingof Science,including W.L. Bragg went on to solve other simple mineral Mineralogy. structuresvery rapidly.This work proceededthrough the 1920s,dominated by Bragg and his coworkers,names M inerab gy and crys tallo g raphy to fire the imaginationtoday: B.E. Warren,who solved the structuresof diopside,tremolite and vesuvianite,a In I 9 12.under the directionof Max von Laue.Walter truly heroic achievement;J. West, who solved the Friedrich and Paul Knipping discoveredthe diffraction structuresof beryl, muscoviteand biotite; W.H. Taylor, of X rays by crystals.This discoverywas immediately who solvedthe structureoffeldspar, a Christrnaspresent seizedupon by the young William L. Bragg and his for an unsuspectingworld. By 1935,the structuresof father,W.H. Bragg,who gavea simpleinterpretation of mostof the commonrock-forming minerals were known this type of experiment Braggs' Law, and derived the (Frg. l0), and W.L. Bragg produceda structuralclassi crystalstructure of halite.Although twenty years earlier, fication for the silicateminerals, based on the polymeri- William Barlow hadproposed that halite wascomposed zation of (alumino-) silicate tetrahedra.T:his tour-de- of sphericalatoms of Na and Cl arrangedin a close- force of structural mineralogy gave an atomistic packedmanner, he had beenignored by the chemists, rationale for the macroscopicphysical properties of who consideredthat NaCl shouldconsist of molecules minerals,and allowed a morecomplete interpretation of 266 THE CANADIAN MINERALOGIST

Mineralogy,geochemistry and petrolo gy

Between 1790 and 1924"an enorrnousnumber of minerals and rocks were chemically analyzed.Geo- KOSTOV chemistrytended to be synonymouswith the chemical analysisof Earth materials,and a large amountof data STRUNZ wasgathered on the compositionof theEarth. However, therewas very little adequateinterpretative work, except STRUNZ for that of Van't Hoff on the gypsum-alhydrite transi- DANA-FORD tion. The detailedchemistry of many of the important rock-forming minerals was not understood,and al- DANA though the generalprinciple of solid solutionhad been known for a long time, the true complexity of the DANA- solid-solution relationships in many mineral groups resistedefforts to understandthem. The key figure in the resolutionof this situationwas 1810 1860 1880 t9m 1920 19.!0 l%0 1980 Victor M. Goldschmidt(Frg. 13). He startedout :rs a petrologist,working on metamorphicrocks in Norway FIc. 12.The increasein the discoveryofnew mineralspecies during the period 19ll-1922. Howeve\ he became over the past one hundredand fifty years;after Skinner& disenchantedwith the currentstate of understandingof Skinner(1980). the chemistryof mineralsand the relationshipsbetween the compositionsof coexisting minerals in rocks. In 1922,he set up a group at Oslo to work on the crystal structuresof minerals and inorganic materials.As a result of this work, Goldschmidt(1937)established his their chemistry,particularly wherecomplex solid-solu- generallaws governingthe distribution of elementsin tions areinvolved. minerals, explaining their behavior in terrns of the Linus Pauling capitalized on Bragg's work, and producedhis famousrules @ig. I l) that form oneof the cornerstonesof modern crystal-chemistry.These con- tributed significantly to the solution and interpretation tttt !t rt !t rt !t t t r!' f I t, !' r, ! of someof the more complex silicate structures;when Waren solvedthe crystalstructure of tremolite(Warren NORSKEcEoLocER: 1929),he used Pauling's third ruleto showthattremolite I containsessential hydroxyl, and that the (OII)- anion ) I occupiesthe O(3) site.Pauling's rules have come under ) F -f criticism at different times as being based on an ) c) unrealistic(i.e.,the ionic) modelof al the chemicalbond. ) I Of course, this is nonsense.The rules are a set of = €l (inductive)generalizations based on theobserved stereo- ) chemistryof a largenumber of crystalstructures, and on ) \J. qe( this basis, are valid observationsaindeed, Burdett & ) (t) (1984) t( McClarnan have arguedfor a molecular-orbital ) .r basisof Pauling'srules. In any even! the rules have ct a ) J -f proven too useful to be discarded,and they [or their generalizationsby Brown& Shannon(1973) and Brown ) o \ol (1981)lremain in extensiveuse today, ) (J I The developmentof powder diffraction occurredin ) .trr 1917,and was an extremelyimportant event for Mner- E alogy. It meantthat mineralscould be identified rapidly ) 1( and reliably, without the great amountof work associ- ) t I ated with chemicalanalysis. This initiated a new era in ) the discoveryof mineral.species (Frg. l2). The rate of ) discovery increasedradically at this point, and it is notablethat this rate has been sustainedin subsequent ) NORGE Bsi decades,primarily by the introductionof new andrapid I ,- ,r - .. ,r - :-1t':j% - - - rt tl,.-a techniquesof characterization,of which electron-micro- probeanalysis has been the mostimportant. Ftc. 13.Victor M. Goldschmidt,geochemist extraordinaire, MINERALS. MINERALOGY AND MINERALOGISTS 267

MINERALOGY OF THREE SIILPHATE DEPOSITS OF NORTHERN CHILE" Menr C. BaNov,Hanaril Unhtersity,Combrid.ge, Moss.

F--E--Gn' { Frc. 3. Sketch of a specimenof zoned sulphates lrom Quetena' showing distribution of the minerals present. 1. Pyrite a,ndszomolnotite 6. Alums 2. Pyrite and halotric.hite 7. Pisanite,var. salvadorite 3, Copiapite 8. Botryogen,rnr. quetenite 4. Jardite 9. Copiapiteand botryogen 5. Parabutlerite 10. Alteredountryrock

Ftc. 14. Paragenesisof sulfateminerals from the Quetanadeposit in northem Chile; after Bandy(1938). atomicstructure of theminerals and the crystal-chemical (Goldschmidt1954), possibly the most important text in behavior of thei constituentelements. This work was the Earth Sciencesthis century. summarized in his seminal book Geochemistrv Contemporaneouswith the developmentof Geo- 26 TTIE CANADIAN MINERALOGIST

Flc. 15.The Skaergaard intrusion in eastemGreenland; from Wager& Brown (1968).

chemistrywas an explosionof work on the synthesisand (but of extremely high quality), and the other of stabilify of minerals and mineral assemblages.During considerablefame. the nineteenthcentury, the advent of the petrographic In the late 1930s,W.C. Bandymapped and carried microscope,when combinedwith extensivefield stud- out detailedmineralogical investigations ofthe copper ies,had led to thedevelopment oftwo schoolsofthought depositsofnorthern Chile, and published a classicstudy on the origin of "crystalline" rocks: the "magmatists" (Bandy 1938) on the paragenesisof the (oxidized) and the "transformationists".Pioneering experimental sulfateminerals associated with thesedeposits (Fig. 14). work hadbeen done by Sir JamesHall ( 176t-l832), but This work is a masterpieceof careful field work and the extensiveinvestigations necessary to examinethe meticulousobservations on both the large scaleand the phasechemistry of granitesand basalts were not feasible small scale;Bandy recorded both broadtrends and local prior to the developmentof the platinum thermocouple variationsin parageneticsequence. It has significantly in 1886.At theturn of thecentury, the magmatic theories influencadcontemporary work on what featurescontrol of Rosenbuchwere well established,and formed an the stability andsequence of crystallizationof minerals. excellentbackground for experimentalphase petrology Perhapsthe bestknown andmost influential work is to begin. The key figure here was Norman L. Bowen, that of Wagerand coworkers(summarized in Wager& who joined the newly established(1906) Geophysical Brown 1968)on the Skaergaardintrusion (Fig. 15) in Laboratoryof the CarnegieInstitute of Washingtonin southernGreenland. This work gaveus an appreciation I 9 I 0, andpublished his seminalwork on theplagioclase for the changein compositionsof solid solutionsof feldsparsthree years later (Bowen 1913).This was an mineralsas a function of conditionsof crystallization, important step toward the more complex systemsthat and emphasizedthat there is an enormousamount of would give rise to his ideasof fractional crystallization information on the petrological history of rocks con- (Bowen 1915, 1928)and the eventualexamination of tained in the detailedcompositional variations oftheir petrologicallyapplicable (r'.e., wet) systems. The impor- rock-forming minerals. Today there is a synergistic tanceof this new areawas that it allowedreal temDera- interaction between field work and experimental tures and pressuresto be assignedto the breakdbwn, (phase-)mineralogy and petrology that augmentsboth melting and crystallizationof both mineralsand rocks, areas,such tlat we arenow usingspecific field mapping as well as the experimentalcharacterization of such to test hypothesesdeveloped from experimentalwork, importantphysicochemical processes as peritectic reac- as well as using experimentalwork to test ideasdevel- tion andcrystal resorption in magmas. opedin the field. While thesegreat developments were occurring in the laboratory,work of fundamentalimportance was con- "MotsRN TNEs": MINERALocy tinuingin thefield. In particular,detailed field mapping, AND EXPERIMENTAL METHODS coupledwith textural and chemicalstudies, revolution- ized ideas on mineral paragenesisand on ways that At the beginning of the 1960s,a technological mineralogical studiescould be applied to the charac- revolution beganin Mineralogy with the development terization of petrological processeson a much more of the electronmicroprobe, and the lastthirty yearshave detailed scale than had hitherto been realized. I will seenan almost continuousintroduction of new instru- briefly describetwo examples,one relatively unknown mental techniquesinto Mineralogy. Work on mineral MINERALS, MINERALOGY AND MINERALOGISTS 269 structureand chemistryhas been greatly enhancedby such that we can now examine minor elements in the application of many spectroscopictechniques to minerals.The chemicalrange for analysisalso has Mineralogy, beginning in the late 1960s.These tech- expanded;now we canreliably analyzefor boron,and niques are of considerableimportance, not the least evenberyllium seemsfeasible in the nearfuture. becausethey can give short-rangestructural informa- tion, and can be used on noncrystalline materials Cry s t al - structur e refinement (glasses,melts, atc.). Below, I outline(very briefly) the usesofeach technique,together with a shortdescription With the adventof the electronmicroprobe, there was of its physicalbasis in the caseof thosetechniques that an explosion in the amount of compositional data areof lessgeneral familiarity. Whatis apparentfrom this availableon commonrock-forming and accessorymin- discussionis that our capabilitiesforthe characterization erals. The resultant thrust to bet0er understandthe of minerals are now far greaterthan what could have generalchemistry of silicate minerals,and apply ther- beenimagined thirfy yearsago. modynamicmodels to the intercrystallinedistribution of elementsorequired a much betterknowledge of mineral structureand crystal chemistry. This need,coupled with Electron+nic rop rob e analys is the commercialdevelopment of automatedfour-circle single-crystal(X-ray) diffractometers,combined to pro- The first instrumentwas designedand built by J.D. ducea rapid expansionof work in mineralogicalcrystal- Castaingin the late 1950s,and within a few years, lography. The basic crystal-chemicalframework of commercialmodels were on the market. The electron olivines (Brown 1978), pyroxenesand amphiboles microproberevolutionized both Mineralogy andPetrol- (Clark et al. 1969,Paprke et al. 1969),micas (Bailey ogy, asthe analysisof mineralsbecame rapid andfairly 1984)and feldspars (Smith 1974ab) was put into place straightforward.Our knowledge of mineral chemistry during this time. At the same time, work greatly improvedgreatly aschemical compositions of minerals expandedin the determinationof unknown mineral were no longer adverselyaffected by exsolution and structures(Moore 1965,1970), for thefrst timeprovid- inclusions.In addition, such microfeaturesas zoning, ing the opportunityto examinethe factorsimportant in exsolutionand inclusionsbecame chemically accessi- determiningthe absolute stability of a structuralarange- ble, and we beganto view Petrologyin a moreprocess- ment. orientedway as the temporal and spatialresolution of Most rock-forming silicatesform at high tempera- our knowledge increased.As the technology of the turesand pressures (l'.e., not at 25oCand I bar),and the instrumenthas improved, detectionlimits have fallen, next stepin understandingtheir behaviorwas to charac-

ro 3660 3 64() 360() z H r RtQUINCV & gl (, 80 F z z U

U = f UI 60 z

-I ol VELOCITY.MM /S FIc. 16. The spectralexpression of Mg-Fe disorderin amphi- x 40 bole:left: Miissbauerspectrum showing contributions from Fefi at M(2) (blackdoublet) and Fe'* at M(l) (unshaded doublet) nd M(3) (sponeddouble0, after Bancroft ar aL (1967); rieht infrared spectrum in the principal OH- stretchingregion, showingbands (A-D) due to local Mgr, Mg2Fe,MgFe2 and Fq arrangements,after Bums & Strens 20 (1966). 270 TTIE CANADIAN MINERALOGIST

terizestructural change as a function of temperatureand seemsto haverecovered from this, and 57Fework now pressure. Structure refinement at high temperature addressessuch diverse topics as next-nearest-neighbor (Camerona al. 1973)and high pressure(Hazen 1976) effects (Bancroft et al. 1983), intervalence charge- showedprevious speculations on structuralbehavior ro transfer(Amthauer et al. 1980),magnetic properties of be faidy accurate.Macroscopic thermal expansion and minerals (Ghose et al. 1987), and surface oxidation compressionproceed primarily by bond-bendingwhere states (uia conversion-electon Mijssbauer spectros- possible.Microscopic thermal expansion and compres- copy), as well as its more traditional areasof valence sion at the coordinationpolyhedron level is inversely stateand site populations. relatedto cation-anionbond-sfen$h; strongly bonded units, suchas (SiOo)groups, show low thermalexpan- Vibrational spe cto scopy sion andcompressibility, whereas more weakly bonded units, suchas (NaOs) groups, show high thermalexpan- sion and compressibility. To a first approximation, A vibrational mode in a crystal will absorbelectro- temperatureand pressurecan be consideredas having magneticradiation if thefrequencies of thevibration and inverseeffects on a crystal structure(Hazen & hewitt the radiationare coincident, and if the excitedvibration 1977).To date,most work in this areahas focused on the measurementof physicalproperties. However, there is considerablepotential in examiningthe vmiation in vibrational characteristicsof sructures as a function of temperatureand pressure,as this shouldafford consid- Ittavdenglh (pm) erableinsight into mechanismsof structuralbreakdown or transition, mechanismsof chemicalreactions in the solid state, and the nature of diffrrsional pathwaysin minerals. A major conceptualadvance in the crystal-chemical study of mineralswas madeby Rossi et al. (1983) and U nguetti et al. ( 1983 ). Theyreal :zed that the lar ge - s c al e structure refinement of rock-forming minerals could give greatly increasedinsight into the crystal-chemical behavior of chemically complex minerals (garnets, olivines,pyroxenes, amphiboles). Of panicularsigaifi- cancewas the derivation ofFeh/Fe2* ratios in pyroxenes and amphiboles,and the recognitionof the importance of unusualconstituents (e.g., Li, Zn) and patt€rnsof order in specificpetrological environments. The combi- o nation of large-scalestrucfure refinement and electron- o tr (and ion-) microprobework promisesto be a powerful |! tool for € a morecomplele characterization ofpetrological o andtectonic processes (e.g., o Ague & Brandon1992). o M ds sb auer spectro scopy

Perhaps the technique with the most immediate impact in the late 1960swas Mdssbauerspectroscopy. This involves the resonantabsorption and emissionof ganunarays by specificatomic nuclei; of most minera- logical interestare 57Fe, 1lesn, ll2sb, l53Euand lqAu. hon is by far the most imporfant species,and Fe in different valence st4tes and at different sites in a structurecan be recognizedand (in many cases)quanti- tatively analyzed(Fig. l6a). This allowsFeYFe2* ratios 0- to be moreeasily measured, and also allows (partial)site 42u, 38q) 94q) 3m0 26(I' pop-ulationsto be derived(Bancroftet a\.1967) in many Wavonumlerfcndl rock-forming minerals. As time went on, Mtissbauer spectroscopywas applied to problems beyond the FIc. 17.Polarized single-crystal infrared spectra in resolutionofthe technique, theprincipal and its reputationsuffered OH-stretchingregion of norninallyanhydrous mantle mine- accordingly(rather unfairly, as this was the fault of the rals: (a) garneL (b) kyanite, (c) olivine, (d) enstatite,(e/ experimenterrather than the method).However, it now zircon,(f) omphacir;afterBell & Rossman(192). MINBRALS. MINERALOGY AND MINERALOGISTS nl

5Hz

-108 -118 p.p.m.from TMS

Frc. 18. Ultahigh-resolution MAs NMR spectrumof highly siliceousZSIvI-S (zeoute), showing 2l of the 24 crystallographicallydistinct si sites resolved; aftetFyfe et aI. (1987).

resultsin a changein the dipole momentof the crystal; stretchingfrequencies of silicategroups for the charac- this givesrise to InfraRed(IR) absorptionspectroscopy. terization of connectivity in silicate glasses(McMillan The Ramaneffect occurswhere electomagnetic radia- I 984),and the useof IR specfroscopyto characterizethe tion is (elasticallyor inelastically)scaftered by a crystal, roleof hydrogen(as OH, H2Oorboth) in aluminosilicate with an ensuingvibrational transition in which energyis glassesand melts (Stolper 1982). absorbedor impartedto thescattered radiation; this gives rise to Raman spectroscopy(McMillan & Hofmeister Nuclear MagneticResorwnce (NMR) specnoscopy 1988).Much early work dealt with the degreeof order NMR involvesthe resonantabsorption and emission in simple oxides (White 1967).However, IR spectros- of (radio-frequency)electromagnetic radiation by an copy in the principal OH-stretching region made a atomic nucleus via the interaction of is magnetic sigaificant impact on the characterizationof order in multipole moment with an applied magnetic field. amphiboles 16b,Bums & Stens 1966)and micas @g. Transition energiesare sensitiveto the local electric- (VedderI 964)after the initial discoveryofthis approach field gradientaround the nucleus,and henceNMR is a by Bassett(1960). Iaier work showedsigrfficant prob- usefirl techniquefor the characterizationof degreeof lems in the basic theory underlying this particular order in (diamagnetic)minerals. The complexity of the application,but it is now being used iricreasinglyto spectrais greatly reducedif the sampleis spun at the characterizethe environmentof hydrogenin minerals, ' 0, where0 is givenby the equation3cos20 both hydrousand nominally anhydrous.The latler useis magic" angle - = giving rise to the technique of considerablegeological significance,as nominally I = 0 (i.e., 0 54.7'), (MAS). MAS NMR anhydrousminerals are a significantreservoir for mantle known as Magic-Angle Spinning NMR to Mineral- hydrogen (Bell & Rossman1992) (Fie. 17), and the hasrevolutionized the applicationof -1980' presenceofhydrogen greatly affects diffusion ratesin ogy. Prior to its developmentin therewas very minerals(Goldsmith 1987).Both IR and Ramanspec- little NMR work doneon minerals.With the application troscopiesare also being usedto (partiatly)characterize of MAS NMR to silicates(Lippmaa et al- 1980),thete -rlz (of the vibrational energydensity of statesin mineralsfor was an explosionof work, first on spin nuclei 2esi calculations(Kieffer 1979). which is the mostimportant) and then on quadrupo- thermodynamic tAl, 23Na l7o. Both IR andRaman spectroscopies are also effective lar nuclei suchas and The strengthof the with noncrystallinematerials, and havebeen important methodis that it can be usedon diamagneticminerals techniquesfor the sfuctural characterizationof glasses. (and in powderedform) and noncrystallinematerials Of particularinlerest here has been the useof principal (glasses,mels, gels);its weaknessis that the absorption 272 THE CANADIAN MINERALOGIST NfiVENUMBER(cu-r ) 20000 10000 8000 5000 q000 2.O o 19 I TREMOLITE ,l Ld fl 1.5 rl (J ;l :l z. ;t rl G ,l ,l m 1.0 It E. 1l f\ c) sf I OJ a I I || m 0.5 \\ t ctr I '."; -..."--'\ 0.0 sm 1000 lgxl 2@ 2500 NRVELENGTH(Nr.r)

Ftc. 19.Polarized electronic absorption spectrum of tremolite; after Goldman& Rossman(1977).

signalsare quenched by the presenceof significant(:1 wherebyan electron is transferredfrom an orbital on one wtVo) paranragneticcomponents. Nevertheless, it has transition metal to an orbital on a locally adjacent been a very important techniquein the derivation of transition metal; (3) cation-anion charge transfer, AI-Si distributionsand local structurein aluminosilicate wherebycharge transfer occurs between a filled anion- minerals: feldspars, Kirkpatrick et at. (1987); feld- orbital and a patially occupiedcation-orbital; (4) tran- spathoidsand zeolites, Figure 18 andFyfeet al. (1987), sitions betweenthe valenceband and the conduction and glasses:Kirkpatrick et al. (1986). band(e.g.,of a semiconductingmineral); (5) transitions Many dynamic processesof interestin Mineralogy betweenthe valenceband and any impurity level within andGeochemistry (e.9., diffusion of speciesin meltsand the band gap, or between an impurity level and the zeolitic minerals)occur on a time-scalethat is accessible conductionband. There have been many attempts to use to NMR spectroscopy(Stebbins 1988). Combined with electronic absorptionspectroscopy for site-occupancy ..inter- the possibilityof characterizingthis behaviorat studies,but with somenotable exceptions (e.g., Fig. l9), esting" conditions(e.g., at high temperaturesfor the this hasnot beenvery successful.However, it hasbeen examinationof motionsassociated with melting and very important to our understandingof coloration magmaticflow: Liu et al. 1987),thistype of application mechanismsin minerals(Burns 1970,Nassau 1983, will be of great geological interest in the future. In Rossman1988). This is a very difficult areaof study; addition,new developmentsin bettercharacterizationof our knowledgeis still only qualitative,and in general, quadrupolarnuclei hold promisefor muchmore diverse very incomplete, as in most cornmon rock-forming applicationsto Earth materials. minerals,several different mechanisms can contribute to the actualcolor seenby the humaneye. However, recent Electronicabs orption spectroscopy improvements in instrumentationmay increase our understandingin this area. When light passesthrough a crysial, it may be absorbedby electronictransitions from theground state Electron SpinResonance (ESR) spectroscory to an excited state of the system.Such transitions commonlyinvolve (l) d-orbitaltransitions in first-row ESR involvesthe resonantabsorption and emission transitionelements (e.g.,Fe2+, Fe3*, Mn2*, Mn3*, V3*, of (microwave)electromagnetic radiation by the elec- etc.): (2) Inter-ValenceCharge Transfer (MT), trons of a paramagneticion. Transition energiesare MINERALS. MINERALOGY AND MINERAINGISTS zt3

TABLE4. REEC@RDINATION IN F-FREE (al ANDF-BEARING PERALKALINE ND SODIUI'I-TRISILICATEGLASSEST XANES EXAFS F-free glasses comotex coordlnatlon l! o z F-bearingglasses o Complex coordinatlon 1A1 g o 6r o Gd-F 2.30 i0 Yb-F 8F 2.23 <2.36> 7300 La-o,F 4 F,4 0x (eV) ENERGY * data from Ponander& Brom (1989a'b)

(b) X-ray AbsorptionSpectroscopy (XAS) AbsoruingAtom W Photoelgctron When X rays are absorbedby an element"there is a gradualchange in the amountofabsorption with energy, intemrpted by a dramatic increasein absorptionat a specific energy that is characteristicof the absorbing [email protected] feature is known as an absorptionedge {@l (Fig. 20a),and is causedby the excitationofan electron @/@P from a deep core level to an empty bound state or a continuumstate. Whenthephotoelectron is ejectedfrom the absorbingion, it may interactwith the local environ- ment (Fig. 2Ob)via (1) strong multiple scatteringthat XANES EXAFS producesa modulationclose to the absorptionedge in (X-ray Absorption Near-EdgeStructure) Frc. 20. (a) K-edgeX-ray absorptionspectrum of Mn in MnO2; the XANES (b) scatteringmechanisms giving rise to the variousparts of region of the spectrum,and (2) a weak single-scattering the spectrumin (a). process that produces weaker oscillations at higher energiesin the EXAFS @xtendedX-ray Absorption Fine-Structure)region ofthe spectrum.One can derive interatomicdistances and coordination numbers ofboth major and minor elements in both crystalline and sensitive to the surrounding crystal-field; hence the noncrystallinematerials (Brown et al. 1988). Only a spectragive information on the characteristicsof the small amount of work has been done thus far, partly local environment,and site occupanciescan be derived becauseof the shorttime that the techniquehas been in (Calas 1988).ESR is applicableonly to paramagoetic use,and partly becauseof the limited availability of the species,primarily ions with an odd numberof electrons equipment(it needsa synchrotronas an X-ray source; (e.g.,Mn2*, Fe3*), and color centers(unpaired electrons althoughsome normal X-ray sourceshave been used.for or holes at "lattice" defects).tn addition, the paramag- suchwork, they are impracticalfor most mineralogical netic speciesmust be very dilute, or elsetheir magnetic and geologicaluses). Ponander & Brown (1989a"b) momentswill interactand result in a broadstructureless examinedthe behaviorof La Gd andYb in silicateand resonance.Thus ESR is a trace-elementtechnique, and aluminosilicateglasses, and derivedcoordination num- has given us most of the information we have on bersand local meanbortd-lengthsaround the rare-earth trace-elementordering in minerals and its possible species(Table 4), the first information of this sort to be sensitivityto temperature(e.g., Ghose & Schindler a-eriveO.They also showed that in halogen-bearing 1969). However, ESR has seenrelatively little use in glasses,there is preferentialcomplexing (Table 4)' and Mineralogy compared with the other spectroscopic here too derived meanbondJengths to specific fgand methods.Perhaps the increasinginterest in trace-ele- types. This sort of work is going to make a major mentbehavior in minerals(promoted by the availability differenceto our understandingof noncrystallinemate- of microbeamanalytical techniques for traceelements) ljralsandthebehavior of traceelements in mineralsand will encourageincreased use of this technique. melts. n4 TIIE CANADIAN MINERALOGIST

FIc. 21. IIRTEM micrographof olivine partially amorphizedby 1.5 MeV Kr+ ion irradiation; a: amorphousdomains the size of displacementcascades in a crystalline matrix (after a doseof 2.55 x l0l2 ionVcm2:b: isolatedcrvstalline domainsin an amorphousmatrix (after 1.7x l0r3 ionVcm2);after Wang & Ewing (1992).

TransmissionElectron Microscopy (TEM) tion of physicalpropertiesof minerals(e.9., magnetism) that play important roles in other areasof the Earth Theelectron microscope was developed in the 1930s, Sciences. but wasnot usedwidely for mineralogicalwork until the A major step forward in the further application of 1970s.At this time, it beganto assumeimportance in the electronmicroscopy toMineralogy was takenby Buseck study of microstructures,as it extendedour powen of & Iijima (1974), who showedthat structureimages of observationway below the resolution of the optical minerals can be obtained at the unit-cell level: such microscope.Fine exsolution-inducedtextures revealed imagescan now be obtainedwith a resolutionof -1 A. tltepresenceof low-temperaturesolvi in manyimportant This gives us a picture of the "real" structure(unlike rock-forming minerals,and the developmentof AEM X-ray andneutron diffraction, which "image" the long- (Analytical Electron Microscopy) played an imporrant rangeaverage structure), and hascontributed greatly to role in quantiffing the chemicalcharacteristics of such our understandingof atomic-scaleprocesses in minerals. sfuctures. Antiphasedomains and $/in domainswere In particular, it has shown the presenceof extended identified in many mineralsthat showhigh-temperature defectsin chainand sheetsilicates (Veblen 1981), and or high-pressurephase transitions. [n particular, an- hasplayed an importantrole in understandinglow-tem- tiphasedomains showwide variationin sizeand texture peraturealteration reactionsin clay minerals @eacor within a specific mineral type, and contain significant 1992).High-resolution TEM alsohas played an impor- informationon thermalhistory. Thus Carpenter (1981) tantrolein workonradiation damage in minerals,atopic showed that domain size in omphacite correlates that has been of significant economic and political strongly with peak metamorphictemperature, the min- interest becauseof is importanceto the problem of erals originally growing with metastableshofi-range nuclear-wastedisposal. It hasbeen possible to tracethe order and then developinglong-range order ylc forma- developmentof structuraldamage with increasingdose tion of antiphasedomains subsequent to initial crystal- of radiation(Fig. 2l), confirmingthe modelof Ewing lization.TEM work on this scaleshould be of increasing (1975) for the final amorphous structure. HRTEM importancein the future, particularly in the interpreta- studieshave still scarcelytouched the large numberof n5 MINERAT.S,MINERALOGY AND MINERALOGISTS .6;i1

1;|:!1::)t- -'- - \-)-1.1 z . I

Frc. 22. How to reat a rock.

many of these larger mental resolution have now resolved mineral reactionsawaiting study, and a much RE-E' oroUt"*t. The ability to analyzetrace samples for numberof theseinstruments are needed within the Earttt ifnsg *a F is now contributingsignificantly to-studles SciencecommunitY. In ; --tl; processes(Satters & Shimizu 1988)' periodictable sdtns is sensitiveto parts9i th9 MTCNOSSAM TECHNIQUES elecfion "OAii"",inaccessible (or only recentlyaccessible) to the microprobe,'fJ;":lit and is importantas a microprobetecnnlque In the past,Mineralogy has focusedo1 fgur lain ;;"" and major light-lithophile elements:H characteristicsof minerals:structure' crystal chemistry' wttiamsrs"sal aio r-i, se ano B-(ottotini er properties'How- i;ilt;& is.an maior-elementchemistry, and physical ii.-tsh).It shouldnot be forgottenthat S^IMS now domg high evir, thingsare changing. Many people-are i.otopi" iechnique;it hasproven very powerful for themselves e/ aL Mineralogy, people who don't consider ?routial i"tofution microprobedating (Compston sedimentolo- gen- minerUo[ists:geochemists, petrologists, r ds2i,;r zonedminerals lwith differenttemporal. geochronologlsts' andas a eists. atmosphericscientists, even erationsof gowth) usingradiogenic isotopes' p"opr6 have realizedthat if you grind up a rock fitt"i" microprobe"..itfrs for stableisotoPes' for analysisof any sort, you lose an enornous alnount it ato a surfacetechnique, and so by-continual to analyze.the of of information(Fig.22).It is far beuer *uf"tit of u surface,he depthprofile of distribution light lithophile SMS individual mineiati for what you want: ;;;iil can be derived' This has made and J.."ntt, t elements(REE^), high-Jield-strength ri-i.""n-t "i.."ntttool in studiesof mineral dissolution "-earth carbon isotopes' elements(IIFSE), oxygen isotopes, weathering(Muir era/ 1990)' upf, *xfna., etc.-ln fact, why analyze-thebulk Aguin,we areundoubtedly losing information *io"Atf X- raYFluore s c enc e bv doine thai; we needmicroprobe methods for this type Synchrotron (SXRF) oi *ottl and we havebeen getting them in the last ten years. by The fluorescentemission of characteristicX-rays long beenused for whole-rock Se c onlary -I on M ass SPectrometry or rock has ";;;;;analysis. The recentavailabilitv (SIMS) "l ry*;i:5:tl?,,1:t"vallowed souic"s Ua synctrotronradiation(cf XAS),has the developmentof a synchrofion X-ray fluorescence SIMS usesa focusedion beamto removeions from low lSXnfi .i"toprobe. This hasthe advantageofvery the sampleand analyzetheir massand chargewith a iu.teto*O signals,and hence is an ideal frace-element rnur, ,#tto."t"t; this was the first microbeamtech- in ;;-iq; Nthough it must still be regardedas.being niqueto allow the analysisof samplesfor traceelements a the developmentstage, SXRF shows prormse^as *l itotop"t (Shimizu et aL 1978,Lovering 1975)' for t u""-"t"rn"nt microprobemethod Q'u et aL 1989) There was some initial trouble in dealing with com- piexed lons, but improvementsin techniqueand instru- thefuture. 276 THE CANADIAN MINERALOGIST

q00 il'lil

35QAA i,...^l' I r/l 30aoa h/|l(i*" 0esaa tt N I aae 15eA

lAAAA

SAAA CHRNNELNUITBER

Ftc'23' KX'ray line PD(E spectrumof a sampreof apatitefrom Durango,Mexico, showing the resolutionof the variousftEE K lines; I AsKa, 2 RbKo, r stra" a yro, 5 InKd 6I-aKa,7 CeKo,, prKcq 8 9 NdKo, t0 kfp, I 1 CeKp,t2 Sm,t(a,13 NdKp, tA CdKc-., 15 Tb.Kq, 16 YbKol and,17 ybKa2: after Durochere t al. (1988\.

Proton- induc e d emiss ion methods scanning techniqueshave now been developed,and trace-elementmapping is now (Teesdale The basic-principles feasible et al. . ofthis groupoftechniques are t993). the sameas those of the electronmicioprobe, except tirat the exciting particlesare protons rathir than electrons. las er- ablation technique s A^sthe massof the proton is muchgreater than the mass of an electron,the bremmstrallqag prlmary contri_ lttre The.availability of lasershas greatly expandedthe bution to the backgroundradiation) is much io*.i in proton-induced lersaliliry of T-y mass-spectrometeriechniques, and X-ray emission;herrce these techniques thereis are much importantdevelopment work currentlvin moresuitable for trace-elementanalysis. protoi_In- progress duc.ed. on microprobeand milliprobesampline tech- X-ray Emission (pDG) is the most *Ar/ieeriating [email protected]). In somearear.,uih us techruque,and has been particularly important"orn-on in the (Y o* et al. 198l), techniquesare fairly mature,and their of trace preciousmetals in ,ulfid. min".al, llalysis applicationto problemsin the EarthSciences is increas- (cabri er al. 1989). In addition, the availabiliw of ing; othersare more in the developmentstage laser high-energy(^40 MeV) sourcesalso allows [e.g., accessioK ICP-MS(Jackson et al. 1,993),lasersamplingfi itable X-ray lines.ofall elementsof the periodic table,making isotopes(Sharp 1990, powell & t

of researchby the scientific community. Theoretical Mineralogyis now arecognizedareaof work, ratherthan somethingthe field persondid when it was snowing,or the experimentalistdid when their equipment was broken. The principal effort has involved attemptsto understandthe structure,crystal-chemisbry and proper- des of minerals at the atomistic level, and further to understand the dynamic role that minerals play in geologicalprocesses.

c rystal- structure aftang ement s

The mostfundamental work is involvedwith attempts to order and understand the plethora of complex structuraldrangements that occurin minerals.The fust step was taken by W.L. Bragg in his well-known classificationof the silicateminerals, in which he setup a hierarchyaccording to the modeof polymerizationof the (alumino-)silicatepart of the structure.The funda- mentalnature of this schememay be seenby comparing it with Bowen'sdiscontinuous reaction series in igneous rocks (Fig. 25); there is a progressivecondensation of the tetrahedra with progressive crystallization, indicating the relations betweentemperature' structu- ral connectivity and stability, with additional Frc. 24. The wanton destruction of minerals by Hawley implications as to the connectivity of tetrahedrain medallistsinvolved in lasersampling for mass-spectrome- magmasat different temperatures'pressures and com- try techniques(from Jacksonet aI. 1993); the sampling positions. is cunently diameterhas gradually been decreasing,and Therewas little furtheradvance until thework of P.B. about10 Pm. Scale bar: 141Pm. Moore, who recognizedthe fundamentalnature of this problem. He attackedthe structuralcomplexity of the phosphateminerals, hitherto an ugly jungle of igao- rance.and showedhow order could be brought to the bewildering variety of structuralarrangements (Moore

ISOIATEDTETRAHEDRA... .OLIVINE .1, I SINGLECHAINS. .PYROXENE 0l DOUBLECHAINS...... AMPHIBOLE 'l' I SHEETS...... MlcA

FnbcnessvE TETRAHEDRALcoNDENsATloN wlrH ESSIVE CRYSTALLIZATIO N

Frc. 25. The correspondencbbetween Bragg's classificationof the silicate minerals(left) and Bowen's discontinuousreaction serie.s (right). 278 TTM CANADIAN MINERALOGIST a AMBLYGONITE- ion PRIMARY Addil s, TRIPHYLITE- LITHIOPHTLITE Addilions, MONTEERASITEsubfrociions sublrocfions -L,it NO OXIDATION 0x l 0ATr0N -Ll' I t - I I f riploldile-rolfeite lerrl sictlsrlfe - slctlerlie METASOMATIC lrcmonllte + fls+- - nolroohillle 'qriphite. I 'rhillockilescorzollfc heleroslte-purpurite C08+ lfiil: - \olluouditef\ ,fNq+, I I | +OH,+tW +0H-,rHrO EARLY phospholcrrite- tovorite o,Polire - ,,l'* reddinqllo_ - lryzhonovslile ludlomlf o rockbridoelle hureoulile frondsliti rZnP+- * [phosph.ophyllila dufrenile rt 5cn0tz|le lqubmonnife(?) -1gs!l- -{ foirfieldlte ozovskite(?l HYDROTHERMAL t messelite clinoslron{ifd 'lr reosohorife .strengito 1gllf - lchildrenile Detmdn|l0 iBq81 Srlt 't loueite {if','.:,tilil' pscudolouelle - rr0scneTl I0 slerortils +gse+- lmoroesi?e tlrunz ifo srilzerile rqnlhorenlle vivion il e cocoronll€ mitrldoflto F - r cqs+ leucoph.osphlle.- -+K+ 0Y8ttn0r tt -+No+ foheYlle .- - +8e8+ lest oue I r!5tou!r LATE cqrbonqfe- opol ils corbonolr-opolitc crondqlIife crondolIifs F6l+.ynt+'l+ hydroridss

Fto. 26a.Paragenetic hierarchies in pegmatiticphosphares; after Moore ( I 973).

1965,1970). Furthermore, he followed this up with a Pauling's rules) nothing to do with the models of detailed parageneticsynthesis (Moore 197:), anO bonding at all. The radii are essentiallythe grand mean showedthat, as in the casefor therock-forming silicates, bond-lengths in crystals, factored into two parts the sequencesof crystallizationin phosphateparagene- (the "radius" of the atoms at each end of the bond) sis arerelated to the underlyingstructural arrangements suchthat their sumsreproduce those grand mean bond- (Figs. 26a, b) and to the effects of oxidation and lengtls; as such, they are model-independentlexcept hydrolysis;truly outstandingwork ! ! for the choice of a "starting radius" (usually for O2)1. They have played an immenselyimportant role in our Crystal chemistry understanding of mineral (and general inorganic) chemistry,particularly in complexstructures (e.g., alrn- pauling The work of W.L. Braggand Linus servedas phiboles, micas), where the combination of crvstal- 1-ggneralbasis for crystal chemistry up until the late structurerefinement and crystal chemistry has b"eo u"ry 1960s.However, the rapid expansion in theamount and powerful. accuracyof crystallographicdata on minerals(and other Various developmentsof Pauling's second rule inorganic materials)caused by the introduction of the (Pauling 1929) have also been of great importancein automatedfour-circle diffractometer neededa more understandingstructural stabilify. Again, this work quantitative basis. This came first with the empirical seemsto have beendriven by the availability of large "ionic" radii of Shannon& hewitt (1969)and Shannon amountsof crystal-structuredata at theend of the 1960s. (1976).I alwaysget a slightly uneasyfeeling herewhen ooionic", The schemeof Brown& Shannon(1973) is now widely I use the word as it seemsto be chargedwith usedin structuralinorganic chemistry and mineralogical such emotional significance for so many people, crystallography.It has played an important role in our whereas the radii in question have (like many of understandingofboth short-rangeand long-range order MINERALS. MINERALOGY AND MINERALOGISTS 279 b

a/6\ r#q LAUEITE (cryslols) JV{, rAil tr,tn2*ref {oH),(Hz0)6 [P04]z. 2Hz 0 2[ru"{Hro)rl'*

crystoltirotion t

H\r+l t{ -_-rr_ | /(;*7\ tt+\'orzo-x ,,x\/{, o/'\* r/v P(0H)ro n[un'* {Hro ).]t* + @ .\v. 1e\ [r.'j touttxro),0]o*

polymerizolion

Ire'itont (H2o), [eo. {oH)r]l'" 2n[Fel*(oH) (Hro), [eo. ton t.] l

Flc. 26b.Progressive structural condensation in pegmatitic fluids; after Moore (1973).

in crystals,and in combinationwith the systematization Thermodyrutmics possibleusing ionic radii, hascontributed greatly to our understandin! of the more complex of the silicate In the 1950s,the recognitionthat therewere compo- minerals. sitional relationshipsbetween coexisting mineral solid- 280 TIIE CANADI,AN MINERALOGIST

CALCUI.ATIONOF CRYSTALPROPERTIES

aIGURAIELV CALCULATEENERGY & ENERGYDERIVATTVES

ELECTRONMETHODS

CLUSTER I-ATTICE MODELS MODELS

Ftc. 27. some theoreticalapproaches to the calculationof the structureand propertiesof mrnelaF. solutions,and that theserelationships seemed sensitive methods propose a specific model (usually of the to externalconditions, led to the introductionofthermo- chemical bond) and usually proceed in a deductive dynamic modeling on a large scale. Classic work by fashionto calculateproperties of interest.Of course,not Mueller (1961) and lcetz (1963) on ferromagnesian all work adheresto this scheme,and indeed it shouldnol silicatesin metamorphicrocks was followed by much Many of the calculationsare of a complexityto obscure work on cotrlmon minerals from a wide varietv of the underlyingphysics and chemistry,and many inves- environments.The generalthrust, of.ou.r., ra, to tigators havechosen to usea more inductive approach, evenfuallyderive geothermometersand geobarometers wherebythey rationalize 'trystallization" observedstereochemical cor- by which thetemperature of of therock relations with qualitativeideas developed from a theo- could be measured.It was soonrecognized that several retical model; this has the advantageof conveying a barrien lay in the way of this goal. Internal (intra- physical-+hemical"feel" for the behavior of complex crystalline) ordering also contributedto the exchange structures. process;with increasedknowledge of long-rangeorder We may summarizethe goalsof muchof this work in in commonrock-forming minerals,this was (in princi- the following way: given an approximateatomic ar- ple) overcome.However, it was graduallyrealized that rangement,we wish to (l) optimizethe atomicarange- kinetics could play a significant role in controlling the mentto give accurateatomic positions, and (2) calculate final chemistry of minerals with regard to intercrys- the (staticand dynamic)propefiies of the structure.We talline and intracrystallineorder, and that the kinetic canrecognize two principal approachesto this problem. aspectsof thesetwo processeswill also be different. I thought about the best way to name these without At somestages in the developmentof this topic, it has causingreligious dispute,and decided that this wasbest seemed that the difficulties were insurmountable. done accordingto the smallestunit treated:atoms et Nevertheless,the last twenfy years have seen the electrons(Fig.27). development of numsrous geothermobarometers, The fust "atom" model for crystal structureswas wherebythe conditionsof equilibration of a rock (or a developedin the 1920s,primarily by Max Born with subsystemwithin arock) canbe calculatedw.ith accura- input from Madelung(1918), and involved a simple cies commonlyapproaching t25oC and 1 kbar. two-bodyinteratomic potential (Born & Iandd 1918). Most subsequentmodels have involved someform of Stntctureand properties of ninerals fwo-body potential. Those who don't like the o'ionic" tradition of this model prefer a Morse-typepotential, This heading subsumesa variety of topics that whereasthe Modified Electron Gas (MEG) model has generallyare given othertitles, and overlap strongly with beenintroduced for the nonempiricaldetermination of other fields (e.g.,thermodynamics). However, they are repulsive parameters.Whichever methodyou choose, groupedhere as they areusually what canbe designated deviations from the Cauchy relationship show that a as "model-dependent"approaches. Thus, rather than central two-body potential is not sufftcient, and all look at a large number of data and develop approachesnow include o'ruleso'(such inductive additionalnoncentral potentials asPauling's rules, ionic radii,2rc.),these of someform. Detaileddevelopments along theselines MINERALS, MINERALOGY AND MINERALOGISTS 281 aresummarizedby Burnham (1990). These modelshave improvedout of all recognitionin the last twenty years. They are now capableof predicting structuraldetails, phonon-dispersionrelations, elastic properties, thermo- dynamicdata and (most impressively) isotope fractiona- tion factors in such anisodesmicstructures as calcite (Doveet a\.1992)afi diopside(Pxel et al. 1991). "Electron" methodswere infoduced into Mineralogy by the pioneeringwork of G.V. Gibbs (Gibbs et a/. 1972).This initially involved the use of qualitative '6 molecular-orbital argumentsto rationalize observed tr 1@oC relations between bond lengths and bond angles in o tetrahedraloxy-anions (particularly SiO{-) in mineral c structures.The successof this approachled to quantita- tive semi-empiricalmolecular-orbital calculations on eoo% smallfragments of silicatestructures, the fragment being embeddedin a field of some sort. Calculations of graduallyincreasing sophistication (see the treatmentby Tossell & Vaughan 1992) have greatly increasedour understandingof stereochemicalvariations and absorp- 1100t tion spectroscopyin minerals.More recently, geatly increasedcomputation power has allowedthe generali- zation of evenab initio methodsto periodic structures. 500 1000 This can be done either by formulating the molecular orbitalsas Bloch functions(Pisani 1987) or by using Wavenumber(cm-l) Local Density Approximation (LDA) methodssuch as the Linear AugmentedPlane Wave (LAPSa) method. Frc.28. Temperature-reduced Raman sp€ctra of glass(100'C) Thesehave beenquite successfulin calculatingelastic and melt (900 and 1100"C)of bulk composition constants,equations of stateand the electronicstructure Na2O.2SiO2.0.027NaAl2O4;the liquidus temperatue is of reasonablycomplicated oxide minerals(Dovesi et al. 850"C.Note the similarity of thespectra of theglass and 1987,Cohen 1991). Among other things, such calcula- themelts; after Seifert et al. (1981). tions areimportant in constrainingmodels of theEarth's core and mantle. Second-orderphase transitions are an important factor in the behavior of many minerals, particularly positional changes,spontaneous strain) of the correct those that show convergentordering of cations (feld- symmetrycan reflect the behaviorof Q. This approach spars,omphacitic pyroxenes, staurolite, etc.). A unified hasbegun to play an importantrole in understandingthe approachto suchbehavior is providedby Landautheory thermodynamicbehavior of suchimportant minerals as (Salje 1991),in which thereis an interactionbetween feldspars,omphacitic pyroxenes, cordierite, etc. ln crystal strucfure and thermodynamicsuia symmetry addition,it has led to considerableinsight into the strucfures.Commensurate theory(Hatch et al. 1987).If pe(r)is the densitytunction behaviorof incommensurate transitions are associatedwith symmetry points in of the high-symmetry phase, and p(r), the density t-space, where the ordered stateis basedon a single function of the low-symmetSyphase (the spacegroup of subgroup-ineduciblerepresentation. However, at arbi- which is an isotropy subgroupofthe spacegroup ofthe trarypoints in ft-space,interaction between two different high-symmetryphase), the difference between these two schemesof order can give rise to a structureresonance be written as Ap(r,T,P....)= density functions can that results in incommensuratebehavior (McConnell Q(T,P...)Ap(r),where Ap(r) is the differencebetween 1978). p(r) andp(r) extrapolatedto thesame conditions as p(r), andQ is designatelwtheorder paramcter.Tlte form of Glessrs axo Mnrs the functionAp(r) is dictatedby the changein symmetry at the transition(it mustfansform asthe activeirreduc- An adequateunderstanding of the physical and ible representation associated with the symmetry chemical featuresof igneous processesis contingent change),and the amplitude of these changesare de- uponan adequateknowledgeofthe meltphase(magma). scribedby Q, the orderparameter [which mustalso have We wish to relate the behavior of such melts to their the samesymmetry properties as Ap(r)1. Although as compositionand structurein the range of physical defined here,Q is a thermodynamicquantity, a change conditionsin which they occur.However, the physical in crystallographicparameters (e.9., site occupancies, conditionsof maly of theseprocesses are particularly 282 T}IE CANADIAN MINERALOGIST

Raman shift (cm-l)

12@ 1000 800 6@ M

NIN stLtcA

N67 NI DISILICATE I U' * b50 NI METASILICATE 6

40 N ryROSILICATE

33 N ORTFIOSILICATE

FIc. 29. Frequencyvariation of the major Ramanbands as a function of silica contentand long-range connectivity in alkaline and alkaline-earthsilicate glasses; after McMllan (1984).

difficult to reproducein the laboratory,and most work RED is XAS; from a structuralviewpoint, suchinfor- has focusedon glassesas melt analogues,as sp€ctro- mationis of particularimportance, as knowledgeof the scopic data on silicate glassesand melts are similar coordinationnumbers of all speciesin a glassprovide (Fig. 28). The study of silicate glasseswas initiated significant consfiaintson the intermediate-rangestruc- by Zachariasen(1932) and Warren (1934),who devel- ture. HrO is an important constituentof many silicate oped the idea of silica glass as a continuousrandom magmas;infrared spectroscopyhas played a significant network. role in characterizingits solubility and speciationin Work on geologicallyrelevant glasses did not really analogousquenched glasses (Stolper 1989). develop into a major thrust until about 10 years €o, Whether a speciesis a network former, a network when spectroscopictechniques (particularly infrarcd modifier or an interstitialconstituent strongly affects the and Raman,NMR, Mdssbauerand X-ray absorption physical properties(e.9., viscosity) of a magma.The spectroscopies)began to be applied to glasssfructure. characterof the coordinatinganions 1e.g., d-, OH-, Cl-, Ramanspectroscopy has been of particularimportance F, H2O)gives information oncomplexing andtransport in deriving information ol local connectivityin silicate of different elements in the melt. These details of (Fig. 29, McMillan 1984) and aluminosilicateglasses. coordinationalso strongly affect our interpretationof MAS NMR hasbeen of particularimportance in resolv- elementfractionation between the melt andcrystallizing ing problems of Al coordination, and in detecting minerals. Until recently, we have had to ignore the unusual coordinationnumbers foi Si that presumably structural aspectsof silicate liquids (and glasses)be- representtransient species quenched from the melt. Of causeof their inractability. However, this situation is particular effectivenessin deriving coordinationnum- now changing,and the advancesofthe past few years bers for larger and lower-valencecations (a.9., Ca Na bodewell for the future. MINERALS. MINERALOGY AND MINERALOGISTS 283

Theasbestos problem

Asbestiform minerals, particularly chrysotile and fibrous amphiboles,have desirablephysical properties for many indusfiial uses,and havebeen used widely as insulatingmaterial, binders and fillers. In addition,numy mining and ore-beneficiationprocesses produce asbes- tiform minerals as a waste product; this asbestosis usually very finely divided, andis easilytransported by wind andwater. It haslong beenrecognized that there is a connectionbetween exposure to asbestosand suscep tibility to cancer,and for this reason,asbestos has been designatedas aknown carcinogenThis whole problem is very complex, not the least becausepolitical issues haveplayed a major role in its development.Neverthe- less,Mineralogy and mineralogiss l;ave played a crucial role in this area,and havebehaved with an objectivity andintegdty (Fig. 30) that someof the otherparticipants would havedone well to emulate. Adequatemineralogical characterization has played an importantrole in defining the sourceof the asbestos (for both scientific andlegal purposes).Even more, for a long time, mineralogistsfought a very difficult battle in trying to investigatethe effects of asb€stosmineralogy on carcinogenicifyin the teethof oppositionfrom other sectorsof the "asbestoscommunity" who seemedmore interestedin propagatingan assumedviewp'oint than in learningthe truth. However,it is now acceptedthat the mineralogical characteristics(particularly amphibole yersas chrysotile) of asbestosare sfrongly related to Frc. 30. Malcolm Ross,hero ofthe asbestos"controversy''and carcinogenicity,allowing a muchmore realistic estimate first recipient of the Mineralogical Society of America's of hazard due to exposure.Problems of asbestosuse DistinguishedPublic ServiceMedal. continue to arise, and mineralogists will hopefully continueto work on them.

ReactiveAcid Tailings ( RATS) ENvrnoNrvreNTALMNgRAI-oGv A feature of many mine sites is the tailings pile' We may divide "environments"into two types: (l) ostensiblyan accumulationof "inert" rock. In sulfide Pristineenvironments (untouched by Humanhand); (2) mines, these tailings piles often contain considerable Perturbedenvironments (e.g., regions adjacentto tail- residual sulfide minerals (pyrite and pyrrhotite are ings piles, smeltingplants, coal-fired electricity-gener- particularly common). These sulfide minerals are ex- ating plants,Kurt Kyser's isotopelab,etc.) tremely reactive in the oxidizing environmentof the All of theseenvitonments may display chemicalor surface;they rapidly weather to produce iron sulfate physicalfeatures that areinimical to local inhabitantsor minerals.These sulfates are generally very soluble;they undesirablefrom a global viewpoint, and it is in the dissolvein vadosegroundwaters and find their way into generalinterest of societyas a whole that we ameliorate local (and not so local) drainagesystems that become any adverseeffects (oxicity, carcinogenicity,physical extremely acid and overly iron-rich. The result is hazard).Minerals are involved in virtually a// of these pollution of local suppliesof water, coupledwith very situations,and both the characterizationofundesirable adverseeffec8 on local aquaticlife. In thelast few years' processesand the developmentof solutionsto many of there has been a significant effort to 0ry to understand theseproblems will generallyfall squarelywithin the the mineralogyand geochemistry of thesetailings piles' domainsof Mineralogy and Geochemistry,with major togetherwith the detailsof their mechanismsof altera- overlap into Soil Sciencesand Geohydrology.We will tion. It is only by understandingthe staticand dynamic briefly considera (very) few examplesthat emphasize characteristicsof these piles that we will be able to the importanceof Mineralogy and Geochemistryin this amelioratetheir deleteriousaffect on the local environ- context. ment. 284 THE CANADIAN MINERALOGIST

MINERAL SURFACES

Rc. 31. Surface-sensitivetechniques that have been impoflant for the surfacecharac- terizationof mineralsover the last ten years.

MTNERAL SLT,FACES atomically sharp conducting voltage-biased tip is broughtclose to the surfaceof a mineral.With a positive When mineralsparticipate in chemicalreactions or bias of the tip, electronstunnel from occupiedstates ooaction" processessuch as adsorption or dissolution,the (surfaceelectronic-energy states) at the surfaceof the oftenoccurs at themineral surface. the interface between mineral to the tip; with a negative bias of the tip, the solid mineraland the mediumof interaction,usually electronstunnel from the tip to unoccupiedstates in the (butnot always)a fluid of somesort. Although this idea valenceband of the mineral surface.The image of the is fairly obvious,it is only ttre last ten yearsthat have spatialvariations in currentgives imagesofthe surface seenan intensivethrust in the studyof mineralssurfaces. at atomic oi near-atomicresolution (Hochella et al. This is primarily becausethe instrumentaltechniques 1989);single adsorbed atoms can be imaged,and there wherebywe can studymineral surfacesat the atomic or is the potential for identifying the chemicalspecies of near-atomiclevel have only beenrecently available. the atom. AFM produces similar-scale images for Overthe past ten years,Auger ElectronSpectroscopy insulators.Essentially, it sensesthe Born-type repulsion (AES), X-ray PhotoelectronSpectroscopy (XPS) (Ho- betweenthe atomsof the tip andthe surface(Fig. 32b), chella1988), various other surface spectroscopies (Fig. and producesan atomic or near-atomicscale "topo- 31), and Low-EnergyElectron Diffraction (LEEDS) graphid'mapofthe surface(Fig. 33) vla the displace- havebeen used for characterizingsurfaces at the atomic mentof the tip. Theselast two techniqueshave given us level.In particular,AES andXPS have been important the capability to examine such processesas crystal- in characterizingoxidation reactions at sulfide surfaces, lization, dissolution, adsorptionand alteration at the and weatheringreactions of silicate minerals,particu- atomiclevel, andin situ, asunlike the elecffonspectros- larly feldspars.However, a major breakthroughcame copies,STM and AFM can be usedin air or water. with the developmentof ScanningTunnelling Micros- This increasein knowledgeof the atomicstructure of copy (STM) and Atomic Force Microscopy(AFM). surfaceshas also led to extensivemodeling ofgeochemi- STM works on electrical conductors.such as native cal processesat or near mineral surfaces.This has metalsand platinum-groupminerals, and semiconduc- generally involved following the path of a proposed tors such as sulfides. As shown in Figure 324 an atomic-scalemechanism and optimizing the structures MINERAIS, MINERALOGY AND MINERALOGISTS 285

(a) STM AFM (b) I .t t SCANNINGTUNNELUNG MICROSCOPY ATOMICFORCEMICROSCOPY

Frc. 32. Surfacemicroscopies. a) Scanningtunnelling microscopy,in which an atomically sharpconducting voltage-biased tip interactswith the surfaceof conductingand semiconductingminerals to produceatomic (or near-atomic)resolution images of the surface.b) Atomic force microscopy,in which a sharptip sensesdtfferences in the "Bom" repulsionbetween the atoms ofthe tip andthe surface,producing an atomicscale'topographic map" ofthe mineralsurface.

at the various stagesvia ab initio molecular-orbital potential, sigaificant improvementsin both {tccuracy calculations(e.9., t asaga& Gibbs1990). The structure and precision are still necessary,as virnrally none of of the intermediateactivated complex will have an them (apart from electron-microprobeanalysis) yet importantinfluence on the rate ofreaction and suchkey approachbulk techniquesin this regard.Nevertheless, featuresas isotopic exchange. Not a lot of work hasbeen thereis an immenseamount of workto do atthe current done as yet in this area, and applicationsto mineral levels of performance,as our knowledgeof trace-ele- stability inthe naturalenvironment will alsohaveto take ment and isotopic zoning is minusculewhen compared into accountthecornmon presence ofbio-organisms and with information availableon major-elementzoning. organicacids (which will presumablymodify the hydro- developments: Inthe last25 years,mineral gen-bondstructure of any activatedcomplex). There is Expertnentat relied too exclusively on the electron greatpotential for much interestingwork in this area. analysis has microprobe.As a result,Mineralogy and Petrology have virtuaily ignoredFe3*/Fe2* ratios and the lightlithophile Fu"ruRE Tlts NEAR elements.The ion microprobeshould rectiS the qitu- atron for light lithophile elements,leaving FeYFe2* as What can we expectduring the next few years,and a significantproblem. Often FeYFe2* canbe measured what things shouldwe be pursuing?Although the most crystallographicallyon single crystals, but we need spectacularadvances are usually unexpected in Science, smaller-scaleinformation than this, and there is great manyimportant directions can be identified(table 5) by priority on the developmentof a microprobemethod for extrapolationof currenttrends. Fe3+/Fe2+.Miissbauer spectroscopyis used on bulk samples,but gammarays have too shorta wavelengthto Microbeamtechniques focus either by lenses or mirrors. In principle' the gamma-raybeam could be collimated to form a "mil- As discussedabove, there has been a proliferation of liprobe", but our current gamma-raysources are too microbeam techniquesfor analysis over the past l0 weakto producean effective microbeam via collimation. vears. In order for most of these to realize their full Here is a challengingproblemfor someone! 286 THE CANADIAN MINERALOGIST

Imaging is an extremelyimportant adjunct of elec- tron-microprobeanalysis, and Back-ScatteredElectron (BSE) imagesand elementmaps now play an import4nt role in studiesof major-elementzoning, mineral inter- growthsand alteration.Similar imagesof othercompo- sitional variables(e.9., trace-elementcontents, isotope ratios)obviously have similar potential, and yet therehas beenlittle work in this area.Trace-element mapping by PIXE is now possible (Teesdaleet al. 1993), but the sensitivity needsto be improved. It is here that the significanceofPIGE and PAA becomesapparent, as in principle,maps ofisotopic variability couldbe produced with thesetechniques. Also of considerableinterest is the productionof Fe3*lFez*maps via "scanning"MOss- bauer spectroscopy.All of these imnging techniques await developrnentin the nert few years.

Applications; As noted above,the light lithophile ele- ments have been virtually ignored in rock-forming mineralsfor mostof the last 30 years.However, careful work hasdocumented the importanceof theseelements in minerals,in somecases tracing enigmatic behavior to the undetectedpresence ofthese constituents (Dutrow er al. l986,Groatetal.1992).Itis obviousthatthe analysis of samplesforH, Li, Be,B (andpossiblyC)mwtbe*ome a nonnalpart of the microprobeanalysis of minerals,and that the next few ye:[s must see an increasein the number of ion microprobes in the Earth Sciences community.

TABLE5. IilMRlANTDIRECTIONS FOR FUTURE |ORK

iIICROBEANilFTHOM Developmntof mthod for Fe"/fol further develoDmntof PIGEand PM I@ging - Fe"/F€* by Sl{S(Scannlng llossbauor Spectroscopy) - lsotoplc varlatlons by scannlngPIGE Applicatlons - EllPaltt be aug@ntedby lilP and sntF

AT0r.flconoERtm Ftc. 33.Atomic resolution images of the {001} surfacein Slte occupenclosof tracg slmnts - IAS, ESR,ltanlnascencg spsctroscopy lizardite.Top: the silicatesheet, showing the hexagonal Zonlng ln nlnqrals - naJor 8nd traca-olmnt zonlng ringsof (SiOa)tetrahedra. Bottom: the hydroxyl groups of - osclllrt0ry zonlng,f.edback sffects theoctahedral sheet, with the underlying Mg atomsvisible; - effEcts of dlffusl0n ln the solld stat€ fromWicks er al. (1992). SURFACES Surfacgstructuro ln sir ud ratar - at atoElc and nano-scalss Adsorptlonol'forolgn'constltuonts - lAS, NllR,sls Blologlcal lnteractlons- sffsctiof bactqrla, blofllos Most of the isotopic microprobesare destructiveat the micrometerlevel. Thus we cannot make repeated CI"ASSESAilD NETTS analyticalmeasurements bn thesame point by diiTerent Structure - charactsrlzltion of lnto@dlat*rlngB ordef techniques(e.9., SIMS ard laser-sampledstable-isotope - coordlnatlon of nlnor ud trace constltuonts elfocts 3nd thelr relatlon to physlcal propertles ratios).Usually, this is not a seriousproblem; however, Dyneic in cases where there is major heterogeneityon a PROCESSIIIIIERALOOY micrometerscale, this can be a significantdrawback. tlatalIed appllcailon of rlnoraloglcrl t6hnlqu6 to orbonsflclatlon Techniquesinvolving radiationemission yia nuclear pm95s6 - oinlElzatlon of loss to talllngg transitions(e.9., PIGE, PAA) do notdegrade the sample, - @val of pollutlng c@ponffts prlor to pJr@tallurgical and this is one of two reasonswhy these techniques pEesslng deservefurther developmentas isotopic microprobes. MINERALS. MINERALOGY AND MINERALOGISTS 287

The same reasoning applies to Fe3*lFe2*ratios. involving both major elementsanl trace elements;in Hundredsof thousandsof analysesof Fe2*-and Fe$- addition, the patterns of zoning of major and trace bearingminerals have been produced by electron-micro- elementsin the samecrystal are not necessarilythe same. probe analysisover tlre last 30 years;much of this data Obviously, these minerals hold a great deal more is ofno lastingvalue. To testideas on mineralbehavior, informationon thecrystallization process than dohomo- one must go back lo completeanalyses done by bulk geneous or monotonically zoned crystals. Do they techniquesin the 1950sand early 1960s.Fortunately, representrapidly changing(oscillating) conditions,or some workers are now taking the effort to analyze do they representnonlinear dynamic systems involving Fe3*lFe2+ratios by "minibulk ' methods,and reasonable- coupled crystallization and diffrrsion? There is much quality data are being producedagain. However, com- scopefor work along theselines. binationof electron-microprobeanalysis with derivation Although conditionsof crystallizationand equilibra- of Fe3*lFe2*ratios by crystal-structurerefinement is the tion are of interest,many investigatorsare now becom- bestwaytogo (atleastatthe moment), andsingle-crystal ing interestedin ratesof cooling (sometimesdenoted by oogeospeedometry"), diffractometersshouldbecome as commonas electron the ugly term as thesehave impor- microprobesfor suchwork. tant tectonic implications.Of particular interesthere is compositionalzoning in minerals.The zoning profile Ordering, zoningand dffision measuredby electron- or ion-microprobeanalysis is a convolutionofthe original zoningprofile (producedby For major elements,the degreeof intracrystallineand crystallization), and the results of subsequentatomic intercrystallineorder can be characterizedvery accu- diffusion prior to the "cut-off'temperature for diffr.rsion ratelyby crystallographic,spectroscopic and microbeam in that mineral. Work on distinguishingthe effects of analyticaltechniques. The currentexperimental need is crystallizationand diffrrsion is now underway(Ganguly to develop similar capabilitiesfor trace elementsand 1991),and shouldprove powerfulin derivingcooling isotopes. rates. The strength of this approachis that it can be appliedto severalmineralsinarock,all ofwhich should Experimentalmethods: Microbeam analytical meth- show the samecooling rate. Tltete is scopefor much odsfor trace-elementand isotopic analysis are currently work herein the next few years. under development,and should improve in both accu- racy, precisionand availability in the near future. The Mineral surfaces primary problemis associatedwith the characterization of intracrystallineorder of traceelements (and possible Althoughit seemsfaidyobvious thatmineral surfaces isotopes).Current techniques available are ESR, various are an area of current anl tutwe expansion,it seems luminescencespectrorcopies, and XAS. Both ESRand worthwhile to make a few commentson aspectsof luminescencespectroscopy are capableof significant particular importance.Although there is much basic improvement,and have the added advantagethat the science to be done, the important applications are equipmentis not prohibitively expensive;however, they evidentright now! Adsorptionof toxic chemicalspecies can only be used to look at "white" minerals(1e., (both natural and industrial) on conrmonsurficial min- mineralspoor in paramagneticspecies). What has been eralsis of greatimportance to manyaspects of Environ- lacking in the past is a vigorous coherentprogram of mental Sciences,and must form a significant area of systematicapplication to well-characterizedminerals. expansionin the funue. In manysurficial and shallow Undoubtedly, such an approachwould stimulate the crustal environments,biological interactionis of great improvementsin spectralinterpretation that are neces- importance,and yet, except for specific well-known saryfor thesetechniques to becomeof significantuse. It examples,has tended to be neglectedby the mineralogi- should also be stressedthat this development may cal comrnunity. We are familiar with the effects and possibly be more difficult than for major elements,as importanceof Ih iobacillusfenooxilans andT. thiooxi- trace elements may occupy conventional sites in a dans inthe oxidationand breakdown of sulfideminerals mineral structure, or they may be associatedwith (although what atomic-scalesurface mechanismsare defects. Nevertheless,it is extremely important to involved?).However, what of the almostubiquitous understandthe structuralmechanism oftheir incorpora- biofilmsand cryptoendolithic organisms? Whatroles do tion, as this will have major implicationsconcerning theseplay in mineral alterationin near-surfaceenviron- their thermodynamicbehavior. ments?There is great potential for symbiosisbe$neen SurfaceMineralogy and Microbiology, with significant Theoreticaldevelopments: Models of simple equilib- implicationsfor the EnvironmentalSciences. rium intracrystallineand intercrystallineorder are well developedfor several minerals or mineral pairs, and Glassesand melts haveled to thedevelopment of numerousgeothermome- ters and geobarometers.However, in somecases, min- Most work to date has focused on the short-range eralscan show extremelyfine-scale complex zoning, structureof glasses,primarily on the frst and second 288 TIM CANADIAN MINERALOGIST

coordination environments.It is obviously important When we treat crystalsfrom any theoreticalviewpoin! thatthis work continuewith anexpanding range of glass we deal with them by exlernally imposingtranslational compositions,and both XAS andtwo-dimensional shift symmetry.We carnotapiori derivethe atomic ilrange- correlated (COSY) MAS NMR spectroscopyshould mentofa crystalfrom any theoreticalapproach, and any play increasinglyimportant roles in such work. How- predictions that we may make are based purely on ever, there is a pressing need to characterizethe analogy with other structuresof the same or similar intermediate-rangestructure of glasses.This is quite stoichiometry.So here is a problemreally worth solving. difficult as some techniquesare not sensitiveat this scale, and others have low resolution becauseof the Cry stallization anl. moryhology structuraldisorder inherent on this scalein glasses.It is possible that differential isotopic neutron scattering Figure 34 showsapage from Goldschmidt'sAtlas of (Gwkell et al. 1991)may be the key to thisproblem, but CrystalForms (Goldschmidt 1913). Many peopleview this is not yet clear, as the experimentsseem quite this asa compendiumof irrelevantinformation. They are difficult to do with su'fficientprecision. wrong; Goldschmidt'sAtlas is a compendiumof infor- Of particular inierest is the local behavior of trace mationthat we arenot theoreticallyadvanced enough to elementsin magmas,as this will significantly affect the understandand interpret. The developmentof an ade- partition of trace elementsbetween melt and minerals. quate mechanistic model for crystallization has to XAS seemshighly suited to this work, and should include the rationalization and prediction of crystal hopefully provide much important information on this morphology,as illustratedin Figure 34. One feels that topic in the next few years. there is a wealth of information on conditions of crystallizationcontained in the morphologyof crystals, Processmineral.ogy if only we could interpretit.

The designof ore beneficiationprocesses has gener- Isotopic order in crystals ally beendone on the basisof bulk chemistry,and little attentionis generallypaid to detailedmineralogy andthe Extensive crystallographicand spectroscopicwork behavior of specific mineralsthrough the total benefi- has shown that both major and minor elementscom- ciation process.There are three principal reasonsfor monly are strongly orderedover nonequivalentsites in oomineral-based" what could be termedas optimization a structure. Furthermore, this order conlains much of a beneficiationpr@ess: (l) reductionof commodity information on the history of the crystal, and affects loss to the tailings, (2) optimizationofenergy expendi- intercrystallineorder. hesumably isotopesshow similar ture, and (3) enhancedremoval of undesirablecomDo- ordering,and it affectsisotope fractionation. However, nentsprior to pyrometallurgicaltreatment. The results no one has yet demonstratedthe presenceof isotopic of (1) and (2) are of direcr benefir to the mill. and ordering in a mineral structure, a problem for the (hopefully) give increasedreturn; process(3) resultsin experimentalist$among us. reducedemission-related problems from the smelter,in accord with both current social mores and Federal THE FRAcIr{ENTATToN oF MINERALocy regulations.It is not clearwhy hocess Mineralogyis not more widespreadand important in this regard at the Thereis an enormousamount of work going on in the presenttime. What is clear,however, is thatincreasingly generalarea of Mineralogy.However, much of it occurs severeFederal regulations on industrial emissionsare in suchdisparate fields that manyof us arenot awareof going to greatly encouragesuch work in the fufire. the full rangeof the subject;perhaps even more serious, our peersin contiguousareas @etrology, Geochemistry, SoMeDIFF.IcULT THINGS To Do etc.) areoften completelyignorant of much of modern Mineralogy, and are under the impressionthat little is In caseanyone thinks that we have solvedall of the going on at all. Here,I will briefly considera coupleof difftcult problemsin Mineralogy,here are some signifi- examples. cant problemsfor a rainy Sundayafternoon. Zeolites Structuralprediction Natural zeolitesare frameworkaluminosilicates that Given an approximateatomic arrangemen!we can occurin a variety of igneous,sedimentaqr and metamor- calculate the accurateatomic anangementand many phic environments.They have long beenof interestto stafic and dynamic physical properties.However, we mineralogists,firstly becauseof their interestingphysi- cannot predict the approximate atomic arrangement cal properties, and more recently because of their from the chemicalformula. We cannotpredict a priori complex crystal structures. Zeolites have intemal the strucfuralarrangements in such simple mineralsas atomic-and molecule-scale channels throughtheir struc- halite or periclase,let alonethe silicatesor the sulfates. tures.This allowsthem to actas nolecukr sieves.which MINERALS. MINERALOGY AND MINERALOCISTS 289

Band 1 Tebl 87

Fg. rro. Frg. rr* Flg. rSt.

Fig. tgz. Ftg. rge Fig. :94.

Fig.!sz.

Fig. rse Fig. ts6.

FiS.t39. Fig. rr8. @

Frg. rlr. Fig.rl+ Fig, t4r. Fi8. r.i3.

Frc. 34. A pagefrom Goldschmidt'sAtlas of CrystalForms (after Goldschmidtl9l3)' 'ITIE 290 CANADIAN MINERALOGIST

clay mineralsin their undergraduateeducation, and there is an undercurrentof feeling that clays arenot ooproper" minerals.The result has beenthat the scienceof clays and clay mineralogy has withdrawn from the rest of Mineralogy, and now has separatesocieties, separate journals and separatemeetings. They have very strong Monocllnlc ties with Soil Sciences,another area with a strong interestin (but not strongties with) Mineralogy.Again, a 1.6d0 the result is that all this work in mineralogyis not seen p 1.t72 as Mineralogy, but as "somethingelse", to the general r 1.694 detrimentof Mineralogy as a whole. D 3.22 lt6 Mineral physics lq 1.14 K'r 4.5 The currentinitiative in Mineral Physicshas led to a rebffi of interestin thephysical properties az d dynarnic av 3.9 behavior of minerals.In addition, the associationwith Geophysicshas been very profitable,in the sameway as the interaction befween Mineralogy and Petrology. However, I feel this thrust has tendedto exclude the chemicalaspects of minerals,and this is a major enor. As indicatedin Figure 35, chemistry play Ftc. 35. What is this mineral?Physical and chemicaldescrip- does a fairly tions of the pyroxenediopside. important role in understandingminerals; the impor- tance of chemistry is also apparent from the rapid developmentof Mineralogy via chemicalanalysis of mineralsin the late eighteenthand nineteenth centuries. It doesseem to be an innatecharacteristic ofPhysics (or permit the passageof somemolecules and the entrap- perhaps physicists) to ignore all other branches of ment of others within their structure. This internal Science.This hastended to producea reactionwhereby atomic-scalestructure also gives them interestingand manypeople concerned withdyzamic aspects of mineral useful catalytic properties.Consequently, the synthesis chemistry (mineral alteration, transport phenomena, and characterizationof new zeolitic compoundshave surface properties and adsorption,etc.) have aligned becomeof greatinterest to somesectors of the chemicat themselveswith Geochemistry,or evenwith Chemistry, industry. This work initially owed much to the general forming subsectionswithin the major Chemicalsocie- work on naturalzeolites done by mineralogists.Indeed, ties. individual mineralogistsstill play prominentroles in the This strong polarization into Physicsor Chemistry field of zeolites,and many investigatorsin the field of (notPhysicscndChemistry) acts greatly to thedetriment zeolitesin the industrialsector have been recruited ftom of Mineralogy. First, the work done is commonly not graduateMineralogy and Crystallographyprogams. visible to the bulk of the Earth Sciencecommunity. Nevertheless,most important zeolite work is now Second,both fields (the Physicsand the Chemistry of. publishedin the chemistryliterature rather than in the minerals) must suffer by not being closely associated mineraloglcalliterature, or in specializedjournals such with each other, (i.e., by having different societies, as kolites, a journal that is "invisible" to most Earth different journals of choice, and different scientific Scientists.Thus although much work by mineralogisrs, meetings). andof interestto mineralogists,is donein thisfield, most Earth Scientistsarc totally unawareof this aspectof Whyhas thisfragmentation occurred? mineralogicalwork. This is not a difficult questionto answer;however, CInyMineralogy someaspects of it may be a little sensitive,as they hinge on what are people's perceptionsof "good science". Clay mineralsare of greatimportance to many areas First, a characteristicof very rapid growth (this is ofthe EarthSciences. They are a major constituentof illustrated both by plants and by crystals) is multiple many types of sedimentaryrock. They are of crucial branching.To quoie a phraseused above, minerals are importancein controlling porosity and permeabilityof the fundamentalmaterials of the Earth, and all Earth aquifersand petroleum reservoirs, they areimportant in Scientistsneed to know about them. The developmenr many areas of geological engineering,and they are of a widevariety of analyticalmethods, and the applica- importantindustrial materials. Nevertheless" most Earth tion of theoreticalmodels and techniques of simulation, Sciencestudents get but a cursory introduction to the haverapidly acceleratedin the last 20 years,and have MINERALS. MINERALOGY AND MINERALOGISTS 291 given rise to all of these"new areas"of mineralogical issue?From the scientific viewpoint, one might argue science.However, the formal Mineralogical commu- that it is a healthy sign of glowth, and that the lack of nity, that is, the major mineralogicalassociations and communicationbetween the subfieldsis somethingthat societies.have beenfar too conservativein their treat- will changewith time. However,it is of greatimportance mentof tlese areas.Rather than recognize that Mineral- from an educationalviewpoint. ogy is going througha periodof rapid expansionand Earth Science departments(along with all other diversification, we have (by and large) retained our departmentsin our Universities) are under increasing traditionalview ofthe science;we havebeen unwilling financial pressurebecause of decreasing(effective) to recognizethese new areas,and have been unwilling suppon from Provincial (State) and Federal Govern- to expand our area of operations (larger journals, ments. This condition is exacerbatedby the (quite subsectionsof our societies).Even worse, some have justifiable) expansionof someareas of Earth Science, attemptedto put limits on what is Mineralogy.Even particularly those heavily involved in Environmental generic geologists like myself have had articles re- Sciencesand issuesof Global Change.As a result of turnedby an editor of a Mineralogicaljoumal with the thesetwo factors"ttre traditional areas ofEarth Sciences commentthat this would more appropriatelybe submit- are under significant pressure.This is particularly true ted to a Physicsjournal. Is it any wonder that younger of Mineralogy,primarily becausethe other subdiscipli- scientistswho are leading new areasof expansionin nesview it asa staticarea where no significantprogress Mineralogy are turning to the Physics and Chemistry is occurring.Above, I havetried to make the casethat societies,organizations that are generally more dy- the latter viewpoint is erroneous.However, it is the fault namic, flexible and forward-looking than ourselves? of us mineralogiss that this viewpoint is common.We Whenasked "What is Mineralogy?",I heardaprominent have not demonstratedthe intellectual vitality of our mineralogist(Gerry Gibbs) answer "Mineralogy is what subjectto therest ofthe EarthSciences; ue haveallowed o'homes" mineralogistsdo." When acting as reviewers,associate it to fragment and find other in Physics, editors, editors and society officials, we would all do Chemistry, and the other subdisciplinesof the Earth 'rehabilitate" well to rememberthese words of wisdom. Sciences.It is up to r,l.rto Mineralogy in Another important factor in this fragmentationof the eyesof the Earth Sciencecommunity while it is still Mineralogy hingeson the relative scientific importance an extantdiscipline. andperceived level ofdifficulty associatedwith various If Mineralogy ceasesto be taught(by mineralogists) aspectsof Mineralogy by practitionerswithout a wide as a specific subjectin undergraduatecurricula it will baseofexperience. Some people involved in thephysics have a very detrimentaleffect on the Earth Sciences. of minerals, chemical modeling, and petrological as- New ideasinvolving mineralswill be slowerin being pectsof minerals,look down on the descriptionof new developedand acceptedby a communitywith minimal minerals as a trivial activrty. This attitude stemsfrom knowledgeof Mineralogy.For example,it hasrecently lack of experience.The characterizationof a new been shown that atrnosphericdust is an important mlneralcan be extremelydifficult from an experimental catalyst for photochemicalreactions in atmospheric viewpoint, and often a very high level of experimental gasesat high latitudes.As a mineralogis! one's imme- expertiseis required,as one is frequentlyworking with diatethought is that the mineralogyof this dust,plus the minimal amounts(sometimes one grain) of material,and associatedsurface properties of the various constituent the mineralmay be (to usea traditionalword) "grungy". minerals,must play a crucial role in this process,as this The secondimportant point is that without description catalysispresumably involves a surfacereaction ofsome and characterizationof new minerals over time, we sort.However, as far asInm aware, no work hasyet been would know nothing aboutminerals at all! Doesanyone done on the mineralogicaland surfacecharacterization really wish to publicly endorsethe view that now (in of this dust.(If I'm wrong aboutthis, andwork hasbeen 1993) we know enoughminerals, and do not need to done, it merely reinforces my point on the current characterizeany more? The reverse effect is alsopresent. fragmentationof Mineralogy). Some people involved in the characterizationof new If Mineralogyis taughtbyanon-mineralogist, ittends minerals have looked askanceat the developmentof to betreated in a cursorymanner, with in-depthcoverage TheoreticalMineralogy, with the view that this 'hon- of mineralsin the areaof expertiseof the instructor,and sense"has little or no connectionto reality, and little or superficialcoverage or total omissionof otherareas. We no direct applicationto "real" minerals.A liule more have all met g&duates from traditional "hard-rocK' tolerance and appreciationof the work done by all schoolswho arewell educatedin "igneous" and "meia- sectorsof tfie communityworking on mineralswould go morphic" minerals, but know next-to-nothing about a longway toward pulling all ofthesebranchesback into "sedimentary'minerals (clays, halides, sulfates, e/c.) or a coherentdiscipline. "ore" minerals(PGM, sulfosalts, etc.), andvice versa.If Earth Scientistsare to function well as scientists,they Theteaching of Mineralogy mustbe conversantwith a// groupsof minerals,and must be knowledgeableabout current analytical methods.It Is this fragmentationof Mineralogy an important is the mineralogist that has this expertise, and the 292 TTIE CANADIAN MINERALOGIST

mineralogistmust teach Mineralogy as a corepan of any chimica e la CristallografiA Pavia,Italy. I thank all of Earth Sciencecurriculum. theseinstitutions for their supportand hospitality.

Generaldisclaimers REFERENcES

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