Structural Hydroxyl in Chalcedony (Type B Quartz)

American Mineralogist, Volume 67, pages 1248-1257,19E2

Structural hydroxyl in chalcedony(Type B quartz)

Clrrrono FnoNoer Department of Geological Sciences Harvard University Cambridge, Massachusetts 02I 38

Abstract

Chalcedony including flint, chert and agate is shown by infrared and X-ray study to contain (OH) in structural sites in addition to severaltypes of non-structuralwater, already recognized, held in associationwith internal surfacesand pores. The content of structural (OH) varies zonally both in chalcedony fibers and in natural and synthetic crystals of the same spectral type as chalcedony. The (OH)-rich zones are more rapidly etched, have lower X-ray reflection angles, lower indices of refraction, and whiten on heating to 550- 600'c. Chalcedonyand its varieties togetherwith colorlessquartz crystals and amethystformed at low temperaturesin associationwith chalcedony, and synthetic quartz crystals, have a distinctive infrared absorption spectrum in the 3200 cm-r to 3600 cm-r region (Type B quartz). A different spectrum in this region is afforded by natural quartz crystals formed at higher temperatures (Type A quartz). The structural (OH) is housed by ditrerent mechanisms in these two types of qrartz, apparently depending on the structural role and availability of Al. The generally fibrous nature of low-temperature natural Type B quartz appearsto be a character deriving from the content of (OH) and its effect on dislocations.

Introduction consisting of orderly alternations of two or of three sets of zones of constant thickness with each set Knowledge of compositional variation in quartz uniform in properties (Fig. 1). The zones can be and of the attendant variation in physical properties described in terms of the relative etching rate of almost wholly relates to single crystals. It is difficult eachset, with the notationH (high),L (low), and M to investigatethese matters in quartz formed at low (intermediate).This type of oscillatory zonation has to ordinary temperatures since it then commonly been earlier recognized from optical evidence occurs as microcrystalline fibrous aggregates,com- (Frondel, 1978). prising chalcedony and its varieties flint, chert, and X-ray agate. In such material the general presence of data much non-structural water and of finely divided Chalcedony, especially flint, gives weak and foreign material precludes the precise measurement broad X-ray powder reflections as compared to of the properties of the quartz itself as distinct from quartz crystals, due to the small fiber thickness, charactersofthe aggregate.The present study was which ranges below 10004, and probably also to undertaken after recognition that the concentric strain associated with the strongly dislocated and zonation typical of chalcedony cavity fillings is twisted nature of the fibers. In chalcedony the accompaniedby a variation in the X-ray interplanar attainableprecision using film in a 114.6mm pow- spacings.This is presumptiveevidence of composi- der camera generally is about -+I in the fourth tional variation in the quartz. significant figure in the measurementof the a and c The zonation in chalcedony is accentuated by cell dimensions. This is not sufficient to recognize etching sawn sectionsin HF or hot alkaline solu- the variation in cell dimensions as a function of tions and by water alone at high temperatures and composition already known in quartz crystals. This pressures. The thickness of the zones varies ran- variation usually appears in the fifth significant domly from submicron dimensions up to the milli- figure or beyond. meter range. The zonation sometimesis oscillatory, In the technique employed here, diffractometer 0003-rxx)vE2llI I 2-1248$02.00 1248 FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY 1249

(CIOS)for which precise measurementsof the cell dimensions have beenreported by Frondel and Hurlbut (1955),were used as internal standardswhen relevant. The gonimeter scanningdirec- tion in all measurementswas up angle. Experimentationgeneral- ly is needed for each sample or reflection to determine the optimum time constant and other instrumental settings.In some samplesdoublets could be resolved without pulse height analysis but with some loss of definition. Less satisfactory data were afforded by moving chart recording at low scanningspeeds.

Flint, chert and zoned chalcedony crushed in bulk gave only single broad reflections. In chalcedony with l:1 oscillatory zoning, however, both the a1 and a2 components of (3142) and of lower angle reflections with sufficient dispersion are resolved into double peaks representingthe H and L components (Fig. 2). The angular separation between the paired peaks of a1 Ql42) varied in different samples up to 0.08" 20. At -90.82" 20 a 0.01" interval correspondsto -0.00014 in a a, (3142). Peak separations of 0.02' or 0.03o 20 and irregularities found in relatively broad reflections observed in reconnaissanceruns with relatively short counting times were checked by reruns with reduced counting errors as estimated from the data of Klug and Alexander (1954). Poorly resolved doublets and

Fig. l. SEM photograph of ditrerentially etched oscillatory zoning in chalcedony. The light bands are approximately I micron wide.

U scanswere mademanually at 0.01"20 intervalsover - the higher angle reflections using total counts over z fixed time. The highest angle reflection in chalcedo- l E ny that generally is sufficiently sharp and strong to trJ - (! be used is q (3142),with 20 CuKo1 90.82". (n Measurementswere made on chalcedonysamples F )z showing the l:1 type of oscillatory zoning, on O samples of flint, chert, and randomly zoned chalcedony crushed in bulk, and on density fractions obtained from zoned chalcedony.

The X-ray measurementswere made on two voltage-controlled Norelco diffractometers using scintillation counters and filtered Cu radiation. The baseline and window settings on the pulse height analyzer were determinedby the method ofParrish 90.70 90.75 90.80 90.85 90.90 and Kohler (1956),using a symmetrical dimunition of the total 20 a, Bl42\ beamintensity rangingfrom 5 to 20 percent with baselinesettings usually above background. Pressed mounts of <10 micron Fig. 2. Paired reflections of at (3142) in chalcedony with l:l powders were employed. Si, and an analyzed quartz crystal oscillatory zoning. 1250 FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY multiple peakswith separationsup to 0.10' 20 were that the compositional variation in chalcedony is observedin somesamples with non-oscillatoryzon- due to (OH) in structural sites. ing and in some density fractions (Fig. 3). In chalcedonythe precision of measurementof The quartz with the lower angle of reflection in reflectionsother than (3142)does notjustify calcu- the paired reflections is found to represent the lation of the cell dimensions and axial ratio to five relatively rapidly etchedH zones.Admixture of Si significant figures. Assuming an arbitrary and un- as an internal standard,using Sial @22)at 88.030" varying value, 1.10005,for the axial ratio, a de- and a1 (333)at 94.952"to measure quartz Ql4D, creaseof 0.01' 20 in a1 Ql42) increasesa by establishedthat the high angle or L component of 0.00042and c by 0.000454. The indicated total the paired reflections has reflection angles close to variation is large as compared to those found in the average20a1 Ql42) value of ordinary qtrartz natural and synthetic quartz crystals (Cohen and crystals (90.829"for CuKol radiation as given by Sumner, 1958; Bambauer, 1961; Frank-Kamen- Frondel (1962)and 90.823"as found in standard etski, 1961, 1962; Frondel, 1962; Tsinober and ClO5). Admixture of a few percent of quartz ClO5 Kamentsev, 1964). as internal standard gave sharp reflections that centered on and enhanced the intensity of the Infrared spectra and water content diffuse L reflections. It seems evident that the It is difficult to identify and quantitatively mea- measurementsrepresent a solid solution series, sure the various kinds of "water" presentin chal- with the L component at or near a limiting composi- cedony. Extendingthe model of Pelto (1956),three tion and the mechanismof compositionalvariation different categoriescan be recognized: therefrom involving a decreasein reflection angle. Infrared spectra obtained from zoned chalcedony (l) Molecular water loosely held in pores and cracks and, and observationson zoning in single ideally, released at relatively low temperatures. The water crystals of reported lost from powdered chalcedony in the range from 100' qvartz, described in following sections, indicate to 200'Cgenerally is from 0.1 to0.4wt.Vo.Pelto (1956), however, has shown that molecular water held in tightly sealedpores can be retained as vapor to high temperatures. (2) Hydrogen-bonded (OH) and (OH) held over a range of bond energies in association with internal surfaces including fiber boundaries,imperfectly crystalline regions adjacent there- to, and dislocations.This (OH) is responsible,together with the molecular water of category l, in part for the very strong continuous absorption centering at about 3440 cm-t in the infrared spectrum of chalcedony. The earlier infrared studies of

U chalcedony by Pelto (1956) and Scholze (1960) identified only "water" of these types. Thermal analyses by Reis (1918), Braitsch (1957),Micheelsen (1966) and the writer (Table l) F [flint] z establish that the bulk of the total water in the chalcedony, l generally in the range from 0.8 to |.6 wt.%ois lost continuously n td up to about 600'C with very little lost, up to a few tenths of a (! percent, in the rangefrom 600oto 1000'C.Weight loss at 1000"C, (t) however, is an arbitrary and imprecisemeasure ofthe total water z l in all categories.Barker and Somner (1974)report from analyses o made by mass spectrometry that "water" in quartz crystals can be retained up to the melting point. (3) Hydrogen-bonded(OH) and (OH) held in structural sitesin the quartz itself, independentlyof the non-structural "water" in categories I and 2, and yielding characteristic infrared band spectra.

The infrared spectrum of quartz crystals in the (OH) region from 3200cm-r to 3600cm-r are of 90.70 90.75 9080 90.85 two distinct types. That designatedhere as Type A 20 a, (31421 includes apparently all natural and smoky crystals Fig. 3. Multiple peaks in a, (3142)in a density fraction with d from hydrothermal veins, Alpine-type crevices, -2.597 (above), and in a bulk sample of randomly zoned pegmatites and other deposits formed at relatively chalcedony(below). elevatedtemperatures. The (OH) content of such FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY

Table l. Water loss in chalcedonv Lehmann (1976b,Table 1). Both types vary somewhat in detail depending on thermal treatment, the content of (OH) and trace elements,and the experi- Donslty 2.6L' 2.590 4/2.56 mental conditions under which the spectra are Mean n L.rt? t.5t3 obtained. Loss at t20oC o.2, o.rB o.?? Infrared spectra were obtained at room tempera- J.os6, r2oo-4ooo nrq 0.49 ture, using unpolarized radiation, through 30 pol- Los6,4OOo-5Ooo 0.48 o.49 o.r9 ished sectionsof chalcedonyincluding flint, chert, l,oss, 5ooo-8ooo 0.02 o.1, 0.09 and agate. Additional measurementswere made on I,oss, 8ooo-toooo o.oo 0.01 o.00 sections cut from the colorless and amethystine quartz crystals commonly found lining the central Total los6 1.r, 1.)O 2.08 cavity in chalcedonygeodes and agates.The turbid- ity of chalcedonyand the strong continuous absorp- Data obtaj,ned on air dried { 40 nicron poudera by bsatlng tion around 3440 crn-r necessitatethe use of sec- to coDstet yeigbt. tions about 20 to 200 microns thick. This is a disadvantagesince the intensity of the band spectra from the quarlz itself is thereby much reduced. The qtartz and the crystallochemical mechanisms by data were obtainedon a Nicolet FT-IR Model7199 which the (OH) is housed have been investigated spectrometer. especiallyby Bambauer (1961), Bambater et al. The main features of the chalcedony spectrum (1961,1962, 1963), Cohen (1960),Kats (1962),and are a broad and strong continuous absorption cen- Chakraborty and Lehmann (1976a,b). In Type A tering at about 3440cffi-r, a distinct band at 3585 quartz Al is a characteristic trace element and stands in an approximately stoichiometric relation to the content of (OH) and alkalies. Synthetic qtartz crystals and both natural and synthetic amethyst have a different spectrum in the 3200cm-t to 3600cm-r region,here called Type B. It has beendescribed by Wood (1960),Kats (1962), Kopp and Staats (1970), Tsyganov et al. (1975), Chakraborty and Lehmann (1976a,b), Kekulawala et al. (1978)and others. In syntheticType B crystals thereis no relationbetween the amountof (OH) and that of Al and alkalies, as found by Kats (1962), Atkinson (1972), and Chakraborty (1976). The t4.l mechanismby which the (OH) is housed is not z clearly established. (f The Type A spectrum is characterizedby strong F E q bands at 3370 cm-l and 3430 cm-r among other z features(Fig. a). The Type B spectrum,as seenin (f both synthetic and natural crystals, is characterized F by a strongband at 3585cm-r, a weak band at 3614 cm-r, and by relatively strong broad bands, in comparison to Type A quartz, at 3440 cm-l and 3400cm-r (Fig. 5). The two types also have some absorption bands in common including overtone and combinationbands at -3200 cm-r and -3300 cffi-l, a faint band at 3595 cm-l, and somewhat variable bands, usually weak or not observed in Type B quartz, at 3565 cm-l and 3370 cm-r. A r"t6vENUtlgERS comparisonof the two types of spectraalso is given Fig. 4. Type A infrared spectra in the 3200cm- I to 3600cm I by Kats (1962,Fig. 4.4) and by Chakraborty and region in natural quartz crystals. 1252 FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY

3440 cm-r totally obscures the underlying band spectra; a variable band at 2325 cm-ldue to liquid COz is often present in addition. The total absorption around 3440 cm-t varies in diferent specimens. It is relatively strong in flint and in fine-fibrous chalcedony and may then virtu- ally obscurethe 3585cm-r band. It also differs in adjacent broad zones in a single specimen. The zones in the micron-scale1:1 oscillatory zonation cannot be separatelyresolved but the bulk spec- U U z trum is identical with that of chalcedony in general. (f, F "Water" content of TypeB quartz oE z In unheated sections of chalcedony and flint the .E F extinction coefficient a3aasvaried in different speci- mensfrom 76 to 150.The correspondingcontent of H-bonded OH in weight percent is approximately 0.01a3aas where d?4qo: absorbancedivided by the sample thickness in cm. (Chakraborty and Leh- mann, 1976a;Dodd and Taylor, 1967).The range of values obtained, 0.7 to 1.5 wt.% H-bonded OH, corresponds roughly to the range of "water" lost thermally by chalcedony up to -600'C. It did not prove possibleto discriminatebetween non-structural "water" and any structural H-bonded OH contributing to the absorption around 3440 cm-t. Sectionsheated for 78 hours at 150',200o, 400'and I.IRVENUIlBERS 500"C showed a small decreasein the total absor- Fig. 5. Type B spectrain the 3200cm-l to 3600cm-r region bance, as found by Micheelsen (1962)in Danish for chalcedony (a and b), natural crystals associated with flint, but there was no resolution of the presumed chalcedony(c and d), and synthetic quartz (e). underlyingstructural bands at344Ocm-r and 3400 cm-t. The absorbancecannot be followed to higher temperatures since the sections turn white and cm-r and an inflection or weak band at 3614cm-r, becomevirtually opaque at 550-600"C.The whiten- both diagnostic of Type B qtrartz, with a faint ing is characteristic of Type B synthetic quartz somewhatvariable inflection or band at 3595cm-r. crystals,as describedby Cohen and Hodge (1958), The associatednatural quartz crystals, usually quite Dodd and Fraser(1965) and Bambaueret al. (1969), small in size and difficult to section, show a sharper and also was observed here in natural Type B and a more detailed Type B spectrum. The absorp- colorless crystals. The thermal whitening is not tion around3440 cm-r is much reducedin intensity observed in natural Type A crystals. relativeto the strong3585 cm-r band, as compared In chalcedony an added band at 3744 cm-r be- to chalcedony,and usually is resolved, depending comes perceptible in sections heated at 400'C and on the thickness and quality of the sections,into increasesin intensity at 600'and 800"C.This bandis separatebands at 3440 cm-r and 3400 cm-r. A due to isolated SiOH groups on surfaces and is weak band at 3565cm-r is sometimesalso seen. formed by the thermal decomposition of more com- In chalcedony the continuous absorption from plex surface (OH) groupings (McDonald, 1956, "water" associated with pores and internal sur- 1957;Iler, 1979). faces is superimposedon the structural 3440 cm-l The measured values for a3aasobtained on ran- and 3400 cm-r bands. An analogousfeature is dom sections of colorless and faintly amethystine found in Type A quartz crystals containing clouds crystals of natural Type B quartz rangedfrom 0.3 to of microscopic liquid inclusions, in which a very 13.5,corresponding to 0.003to 0.13wt.VoH-bonded strong continuous absorption centering at about OH. In Type B syntheticcrystals the content of H- FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY 1253 bondedOH generallyis well over 0.001wt.Vo, with Prior to optical examinationthe density fractions were extract- l10oC, immersed in water, blotted dry, high values of 0.05 indicated by the data of Dodd ed in acetone, heated at and stored over water. With decreasing fiber thickness and and Fraser (1967), from a35so,and of 0.059 (infra- increasingrandomness offiber arrangement,the measurementof red) or 0.046 (thermal) by Godbeer and Wilkins <.rbecomes difficult and ultimately only the mean index of (1977).Type B crystals in general appear to contain refraction can be measured. Measurementsof e are unreliable; more "water" than natural Type A colorless and the angular divergence of the fibers from parallelism (Braitsch, oftwisting around the direc- smoky crystals. These usually contain less than 1957)and the common occurrence tion of fiber elongation, [1120], contribute to the well known 0.001 wt.Vo H2O, although 0.028 wt.Vo has been apparentlow birefringenceof chalcedonyas comparedto quartz reported in (OH)-rich zones in Type A qtartz crystals. (Bambauer, 1961; BambatJeret al., 1961, 1962, 1963). The fractionation yielded very small samples at the high and low ends of the range. About 50% of the total samplefell in the range from roughly 2.604 Density and optical properties to 2.617in Sample1, and from 2.591to 2.605in the The values reported in the literature for the Oregon sample. Optical examination showed that density and the indices of refraction of chalcedony the fractions, especiallyin the middle range, con- vary downward over a wide range from the nominal tained a large proportion of composite grains made values d 2.651 and

The size fraction below about 5 microns was removed by sedimentationin water. The remaining bulk sample was rapidly blotted dry to a flowing consistency and was stored over water before fractionation. The density change of the temperature controlled liquid over the dilution range, as obtained by pycno- metric measurements, was initially calibrated by the use of quartz of precisely known density (CIOS)as internal standard. A very small final float fraction differing significantly in density from the final chalcedony sink fraction was obtained from Sample l. It consistedof melanophlogiteand two unidenti- fied platy silica minerals, possibly silica hydrates. Cristobalite DENSITY was not identified in this fraction or in any chalcedony sample Fig. 6. Variation in <.ras a function of density in chalcedony. examined. Solid lines represent Sample 1; dotted lines Sample 2' FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY

the omissionof Si with accompanyingsubstitution of (OH)4 for Oa, indicate that the entranceof 0.5 wt.Vo structural (OH), which is beyond any (OH) content so far found in quartz crystals, produces changesin the mean index of refraction only in the fifth significantfigure. The X-ray reflection angles of the quartz are independentof the porosity and offer a direct means of measuring the H and L components.The o1 (3142) reflections of the nine density fractions of LJ sampleI were recordedagainst Si by both moving F chart and manual scanning methods. The fractions F z with the highest bulk density and ar, composing l about 2Voof the total sample, gave relatively sharp E td singlereflections at a high angle, near 90.82', and (! evidently consist largely of L components. The U) z middle range inhomogeneous fractions gave rela- l o tively broad irregular reflections with a poorly C) resolved but verified asymmetric doublet appearing in a fraction at d 2.597 (Fie. 3). The two lowest densityfractions, composing about I percentof the sample,gave extremely broad irregular reflections whose center line could not be precisely located. The evidence suggests that the fractionation has effected a small separation of the H and L components,with the H componentshaving either a lower true density or a higher characteristicporosity. 90.70 9075 90.80 90.85 Correlations with zonedsingle crystals 20 a, (3142) (OH), The content of Al and alkaliesoften varies Fig. 7. Paired reflections of ar (3142) in zoned Type A quartz spatially within single crystals of natural and syn- crystals with unlike proportions of H and L zones. thetic quartz, both in the growth loci of the external faces and in thin zones concentric to the growth surfaces.The latter type of compositionalzonation, (OH) and lower indices of refraction than the bulk as seen in sawn and etched sections, has been of the crystal. The zonesturn white or milky when describedby Leydolt (1855),Weill (1931),Shin- heated to about 550'C or more. The zoning is Piaw (1945),and especiallyBambauer et al. (1962, ascribed to fluctuations in the growth, the (OH) 1963).The latter authors also establisha relatively content increasing with increasing rate, as also high content of (OH). The zones are differentially found by Chakraborty (1976)for unzoned synthetic etched not only by HF but also by water at high crystals. temperaturesand pressures(Kennedy, 1950).They An identical zonation is found in the small color- also are accentuatedby X-ray irradiation (Frondel, less Type B qtartz crystals that commonly line or 1945;Cohen, 1960;Bambauer et al., 1962. 196i. fill the central cavity in chalcedony geodes and The rapidly etched zones in two Type A Brazilian agates.Photographs of such geodesand agatesare crystals examined here had lower indices of refrac- given by Lund (1960)and by Murata and Norman tion, as seenby movementof the Becke line in thin (1976).In many instances,such as the chalcedony sections, and had lower X-ray reflection angles for geodesfrom Tampa, Florida (Lund, 1960;Zeitner, a, Qr4DGie. 7). 1979;Strom et al., 1981)and Keokuk, Iowa (Van Type B synthetic crystals containing a series of Tuyl, 1916),the crystalshave formed from circulat- thin zones parallel to the (0001) growth surfaces ing ground water at essentially ordinary tempera- have been described by Dodd and Fraser (1967). tures. The crystals examined here were identified as The zoneswere shown to have a higher content of Type B by infrared spectra(7 specimens)and, with FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY 1255 less certainty, by turning milky or white when quartz crystals and quartz fibers also is involved in heatedat 550"C(15 specimens).The crystals often the matter. In quartz crystals the growth rates along contain scatteredzones up to 30 microns in thick- the three-fold symmetry-equivalent directions ness that run parallel to the rhombohedral faces. (tt7O) are equal; in quartz fibers one direction of The zoneshave lower indicesof refraction,as seen this three-fold set is dominant, yielding the fiber by the Becke line effect under the microscope,are elongationalong [1120] commonly observed.The differentially etched, and turn white at 550'C. (OH) content of the quartz may be the controlling Zoned samplessuitable for X-ray work could not be factor here. In synthetic quartz the (OH) content found. The depositionfirst ofchalcedony fibersand weakensthe crystal, by disruption of the Si-O-Si then of single crystals appearsto be a continuous network through the substitutionof (OH), promot- process.The presumptionis strong that the zoning ing plastic deformation (Griggs and Blacic, 1965; in the chalcedonyis carried on in the crystals by the Jones,1975; Blacic,1975; Kekulawala et aI., 1978) sameprocess. and decreasingthe mechanicalQ (Dodd and Fraser, Although the evidenceis piecemeal,the rapidly 1965;Chakraborty and Lehmann, 1976).The intro- etched H zones in Type B quartz crystals and duction of structural imperfections attending the chalcedonyappear to have the higher(OH) content, substitutionof (OH) in chalcedony similarly may lower X-ray reflection angles, lower indices of accountfor the developmentof the screw disloca- refraction and, unlike Type A crystals, whiten at tions that, in the first place, causethe development about 550'C or more. of a one-dimensionalfiber instead of a three-dimen- sional crystal in quartz (Frondel, 1978) and in Discussion whisker crystalsgenerally. In natural environments Type B quartz predomi- Temperatureseems to be an indirect rather than a nates at low to ordinary temperatures.The control- direct factor in the formation of Type B quartz ling factor may be the chemical composition of the fibers since Type B synthetic crystals have been crystallizing silica solution with reference to the grown up to at least400'C. The experimentalhydro- presenceof ions, especially Al, needed to effect thermal crystallization of silica gels indicates that Type A valence compensation.Al is strongly hy- the upper limit for the formation of quartz fibers is drolyzedor polymerizedinto basicpolycations over about 250'-300'C (White and Corwin, 1961),with the pH range common to meteoric waters and ocean singlecrystals, of unknown spectraltype, formed at water, renderingit unavailablefor entrancesubsti- higher temperatures.This may reflect the thermal tutionally or interstitially into the quartz structure. stability of the dislocation system controlling the The content of dissolved uncomplexedAl ions in fiber growth, as is suggestedby the very much such environmentsis below 1 ppm (Bell and Hem, lower incidenceof dislocation-controlledstereospe- 1978;Iler,1979).Temperature also may be a factor. cific twisting in quartz formed at high temperatures Dennenet al. (1970)report that the solubility of Al (Frondel,1978). quartz with decreasingtemperature, in decreases Acknowledgments with values as low as -20 ppm indicated for qtnrtz Labora- formedat -100"C. The actualtrace element content I am indebted to Dr. David Bish of the Los Alamos tory, at the time in the Department of Geological Sciencesat of Type B natural quartz is not known. The report- Harvard, for aid in obtaining the infrared spectra. Dr. GeorgeR. ed analyses of chalcedony are not trustworthy Rossmanof the California Institute of Technology kindly made becauseof the general presenceof finely divided independentmeasurements of the infrared absorbanceof certain foreign material. quartz sections. The formation of fibrous quartz (chalcedony) References insteadof single crystals is influenced by the degree Atkinson, W. W. (1972)Experiments on the synthesisof high- of supersaturation and the rate of growth, with purity quartz. Ph.D. thesis, Department of Geological Sci- fibrous quartz favored by high supersaturationand ences, Harvard University. high growth rates (White, Brannock, and Murata, Bambauer,H. U., Brunner, G. O., and Laves, F. (1961)Beo- 1950;Oehler, 1974).The formation of single crys- bachtungeniiber Lamellenbau an Bergkristallen. Zeitschrift tals following the deposition of chalcedony may fiir Kristollographie,I 16, 173-181. Bambauer, H. U. (1961) Spurenelementgehaltund 7-Farbzen- then result from the decreasein supersaturationand tren in Quarzenaus Zerrkluften der SchweizerAlpen. Schwei- growth rate attendingthe final depletion of the silica zerische Mineralogische und Petrographische Mitteilungen, solution. A crystallographic distinction between 4r.335-369. 1256 FRONDEL: STRUCTURAL HYDROXYL IN CHALCEDONY

Bambauer, H. U. (1962) Wasserstoff-gehaltein Quarzen aus Griggs, D. T. and Blacic, J. C. (l%5) Anomalous weakeningof Zerrkluften der Schweizer Alpen und die Deutung ihrer re- synthetic quartz crystals. Science, 147, 292-295. gionalen Abhiingigkeit. Schweizerische Mineralogische und Heatherington, G. and Jack, K. H. (1962) Water in vitreous PetrographischeMitteilungen, 42, 221-236. silica I. Influence of water content on the properties of Bambauer, H. U. (1963)Merkmale des (OH)-Spectrum Alpiner vitreoussilica. Physical Chemistry of Glasses,1,129-133. Quarze (3 pr-Gebiet).Schweizerische Mineralogische und pe- Iler, R. K. (1979)The Chemistry of Silica: solubility, polymer- trographischeMitteilungen, 43, 259-268. ization, colloid and surfaceproperties, and biochemistry. John Bambauer,H. U. (l%9) Light scatteringof heat treatedquartz in Wiley and Sons,New York. relation to hydrogen-containingdefects. American Mineral- Jones, M. E. 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