Eur. J. Mineral. 1997,9, 623-651

Nomenclature of amphiboles Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names

BERNARD E. LEAKE (Chairman) Department of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ, U.K.

ALAN R. WOOLLEY (Secretary) Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, U.K. C.E.S. ARPS* (The Netherlands; retired December 1994) W.D. BIRCH* (Australia; from January 1995) M.C. GILBERT (USA; resigned 1994) J.D. GRICE (Canada; * from January 1995) Mineral Sciences Division, Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, Ontario, Canada KIP 6P4 EC. HAWTHORNE Department of Earth Sciences, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 A. KATO Department of Geology, Natural Science Museum, 2-23-1 Hyakanin-cho, Shinjuka, Tokyo 160, Japan HJ. KISCH Department of Geology and Mineralogy, Ben Gurion University of the Negev, Beer Sheva 84105, PO Box 653, Israel V.G. KRIVOVICHEV Faculty of Geology, St. Petersburg University, University Em. 7/9, 199034 St. Petersburg, Russia K. LINTHOUT Department of Ore Geology, Petrology and Mineralogy, Institute of Earth Sciences, Free University, Boelelaan 1084, 1081 HV Amsterdam, The Netherlands J. LAIRD Department of Earth Sciences, College of Engineering an Physical Sciences, University of New Hampshire, Durham, New Hampshire 03824, U.S.A. J. MANDARINO* (Canada; retired December 1994) W.V. MARESCH Institute for Mineralogy, Westfälische-Wilhelms Universität, Munster, Corrensstr. 24, D-48149 Munster, Germany (now: Institute of Mineralogy, Ruhr-Universität, Universitätsstr. 150, D-44801 Bochum, Germany) E.H. NICKEL* (Australia) N.M.S. ROCK (Australia; died February 1992)

* Indicates a non-voting official of the CNMMN

0935-1221/97/0009-0623 $ 7.25 © 1997 E. Schweizerbart'sche Verlagsbuchhandlung. D-70176 Stuttgarl Downloaded from http://pubs.geoscienceworld.org/eurjmin/article-pdf/9/3/623/4004120/623_gseurjmin_9_3_623_652_leake.pdf by guest on 24 September 2021 624 B.E. Leake et al.

J.C. SCHUMACHER Institut fur Mineralogie-Petrologie-Geochemie, Universität Freiburg, D-79104 Freiburg i.Br., Germany D.C. SMITH (France; resigned 1994) N.C.N. STEPHENSON Department of Geology and Geophysics, University of New England, Armidale, New South Wales, 2351, Australia L. UNGARETTI (Italy; resigned April 1993) E.J.W. WHITTAKER 60, Exeter Road, Kidlington, Oxford, OX5 2DZ, U.K. G. YOUZHI Central Laboratory, Bureau of Geology and Mineral Resources of Hunnan Province, Dashiba, Kunming, PR. China

Abstract: The International Mineralogical Association's approved amphibole nomenclature has been revised in order to simplify it, make it more consistent with divisions generally at 50%, define prefixes and modifiers more precisely and include new amphibole species discovered and named since 1978, when the previous scheme was approved. The same reference axes form the basis of the new scheme and most names are little changed but compound species names like tremolitic hornblende (now magnesiohornblende) are abolished and also crossite (now glaucophane or ferroglaucophane or magnesioriebeckite or riebeckite), tirodite (now man- ganocummingtonite) and dannemorite (now manganogrunerite). The 50% rule has been broken only to retain tremolite and actinolite as in the 1978 scheme so the sodic calcic amphibole range has therefore been expand­ ed. Alkali amphiboles are now sodic amphiboles. The use of hyphens is defined. New amphibole names ap­ proved since 1978 include nyboite, leakeite, kornite, ungarettiite, sadanagaite and cannilloite. All abandoned names are listed.

Key-words: amphibole nomenclature, crossite, dannemorite, tirodite.

Introduction of the main problems that had been dealt with pre­ viously; (4) representation included the principal This report was produced in response to a motion proposer to the CNMMN of an improved nomen­ at the IMA 1986 meeting in Stanford, California clature scheme; (5) representation was across the asking the CNMMN to produce a more simplified various fields concerned with amphibole nomen­ amphibole nomenclature than that currently ap­ clature from crystal-chemists, metamorphic and proved which dates from 1978. The 1978 nomen­ igneous petrologists to computer experts and ordi­ clature (IMA 78) took over 13 years to formulate; nary broad-based petrologists. There were 18 vot­ a quicker response was attempted this time. ing members when the major framework of the re­ To ensure a fresh look at the nomenclature vised scheme was approved. scheme the Chairman of the Amphibole Subcom­ The committee circulated over 1000 pages mittee, Prof. B.E. Leake, with the agreement of over nine years, and considered in detail all pro­ the CNMMN officials, completely reconstituted posals made to it. Views were expressed that the committee so that (1) representation was more because the amphibole system is so complicated, international; (2) more than 80% of the voting adequate representation cannot be made with two- members of the committee were not members of and three-dimensional diagrams whereas four var­ the committee which produced the 1978 report; in iables can represent the system adequately. How­ addition, none of the CNMMN officials was on ever, the committee, by a very large majority, the 1978 committee; (3) three members were re­ wanted to retain conventional nomenclature tained from the 1978 committee to ensure that diagrams because they are easier for most scien­ there was some continuity and collective memory tists to use. The committee considered a range of

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different naming schemes, but none was judged (1982), Hawthorne (1983) and Anthony et al overall to be sufficiently better to justify abandon­ (1995) from which adequate general background ing the main basis of IMA 78 which has been summaries can be obtained. widely accepted and is capable of simplification to provide an improved scheme. It must be re­ General classification of the amphiboles membered that over 95% of all amphibole analy­ ses are currently obtained by electron microprobe As with the IMA 78 scheme, the proposed nomen­ with no structural information, no knowledge of clature is based on chemistry and crystal symme­ the oxidation states of Fe, Ti and Mn, the H2O try; when it is necessary to distinguish different content or how the site populations are derived. polytypes or polymorphs, this may be done by What follows is a nomenclature scheme, not one adding the space group symbol as suffix. Antho- to determine at which position the ions really are phyllites with Pnmn symmetry (as distinct from located. the more usual Pnma symmetry) may be prefixed The proposed scheme involves reducing the proto. number of subdivisions, especially in the calcic The classification is based on the chemical amphiboles, making the divisions generally fol­ contents of the standard amphibole formula v low the 50% rule (whereas IMA 78 uses divisions AB2C^T^ O22(OH)2. It is to be noted however at 90%, 70%, 66%, 50%, 33%, 30%, and 10%), that possession of this formula does not define an and making the use of adjectival modifiers (ad­ amphibole. An amphibole must have a structure ditional to prefixes which are part of the basic based on a double silicate chain: a biopyribole names) optional. The new scheme has over 20 consisting of equal numbers of pyroxene chains fewer names than IMA 78 and involves the aboli­ and triple chains would have this formula but tion of only a few commonly used names such as would not be an amphibole. crossite. End member formulae defined and ap­ The components of the formula convention­ proved in IMA 78 are generally retained although ally described as A, B, C, T and "OH" correspond the ranges to which they apply have often been to the following crystallographic sites: changed. Numbers are ions in the formula unit. A 1 site formula unit; The principal reference axes of IMA 78, name­ B 2 M4 sites per formula unit; ly Si, NaB and (Na+K)A (see below), are retained, C a composite of 5 sites made up of 2 M l, 2 but the primary divisions between the calcic, M2 and 1 M3 sites per formula unit; sodic-calcic and alkali (renamed sodic), amphi­ T 8 sites, in two sets of 4 which need not be boles have been adjusted to divisions at NaB distinguished in this document; < 0.50 and NaB > 1.50, instead of NaB < 0.67 and "OH" 2 sites per formula unit. NaB > 1.34. Previously, the amphibole 'box' was divided into three equal volumes with respect to The ions considered NORMALLY to occupy NaB. The new scheme enlarges the sodic-calcic these sites are in the following categories: amphiboles at the expense of the calcic and sodic 0 (empty site) and K at A only amphiboles (Fig. 1) in order to make the divisions Na at A or B at 50% positions. Ca at B only As with the 1978 scheme, the problem of what L type ions: Mg, Fe2, Mn2, Li and to do with analyses in which only the total iron is rarer ions of similar size known (and not its division into FeO and Fe2O3) such as Zn, Ni, Co at C or B has been left to individual judgement although a M type ions: Al at C or T recommended procedure is given. This means that Fe3 and more rarely again an analysis may yield different names de­ Mn3, Cr3 at C only pending upon the procedure used to estimate Fe3+ High valency ions: and Fe2+. It clearly would be advantageous for Ti4 at C or T naming purposes if the recommended procedure Zr4 at C only were followed even if other procedures were used Si at T only for other purposes. Anions, OH, F, Cl, O at "OH" General works dealing with the amphiboles include Deer et al. (1963, 1997), Ernst (1968), M type ions normally occupy M2 sites and so Chukhrov (1981), Veblen (1981), Veblen & Ribbe are normally limited to 2 of the 5 C sites. Excep-

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Eckermannite Nyboite NaNa2(LM4)Si5AI3022(OH)2 to

Magnesio-arfvedsonite 1.00 (Na+K)A Ferric-nyboite NaNa2(L2M3)Si6AI2022(OH)2 1.00 (Na+K)A ,8.00 Si 2.00 NaB 2.00 Nac 5.00 Si DNa2(L3M2)Si8022(OH)2 Glaucophane

Magnesioriebeckite pNa20-2M3)Si7AIO2^

— 2.00 Nac W.00(Na+K)A m€plPli£^^^ 1.50 Na WÊÊÊBSÊÊΛ §2.00 NaB -^~ B sodic BβÖ %5.00Si amphiboles HHHi

1.50 Na fΛ^M^^sij 1.00 Na, 0 B Na(NaCa)L MSi AI0 (OH) 1 4 7 22 2 Na(NaCa)L3M2Si6AI2022(OH)2ft Na(NaCa)L2M3Si5AI3022(OH)2 inesiokatophorite ΠHHI

sodlc-calcjc 1.00 Na> amphiboles 0.50 Na, D(NaCa)L4MSi8022(OH)2 |D(NaCa)L3M2Si7AI022(OH)2M(NaCa)L2M3Si6AI2022(OH)2|D(NaCa)LM4Si5AI3022(OH)2- B r Winchite [ Barroisite ^^^^^^^^^^S^^

5.00 Si

0.50 Na 1.00 (Na+K)A 1.00 (Na+KJ^^^&M l^^^^l^^p^^^^^^KiS^^PPfS ^ 0.00 NaB NaCa (L M )Si AI 0 (OH) calcic 0.50 (Na+K) J^^ßf^MSESßWf|f| | NaCa2L5Si7AI022(OH)2^βNaCa2(L4M)Si6AI2022(OH)2 EEß 2 3 2 5 3 22 2 amphlboles A Pargasite^pS Magnesiosadanagaite Magnesiohastingsite 0.00 Na„ ±8.00 Si . 7.00 Si '6.00 Si ΛváOO Si , \Jn.i0.00 (Na+K) 0.00 (Na+K)A i A DCa L Si 0 (OH) DCa2(L M)Si AI0 (OH) DCa (L M )Si AI 0 (OH) 2 5 8 22 2 4 7 22 2 2 3 2 6 2 22 2 0.00 Na B Tremolite Magnesiohornblende Tschermakite DCa2(L2M3)Si5AI3022(OH)2

M = AIVI, Fe3+ # Mg end members are named L = Mg, Fe^,2+ \ Mn Al,v OH = OH, O, F, Cl O hypothetical end members cations per 24 O, OH, F, Cl D = empty Λ-site

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tions may occur to the above "normal" behaviour Fe3 and Fe2 values reasonably close to the true but are ignored for the present purposes of nom­ determined values in 80 % of the analyses enclature. studied, excluding kaersutites, for the Throughout this report superscript arabic num­ calcic, sodic-calcic and sodic amphiboles. If this erals refer to ionic charge (oxidation state) e.g. sum is adjusted to include Li and Zr i.e. Fe2; superscript roman numerals to coordination (Si+Al+Cr+Ti+Zr+Li+Fe+Mg+Mn) = 13 and for numbers e.g. AlVI; and subscript numerals to num­ the Mg-Fe-Mn-Li amphiboles the sum of bers of atoms e.g. Ca2. (Si+Al+Cr+Ti+Zr+Li+Fe+Mg+Mn+Ca) = 15 is To take account of these facts it is recom­ used, then only the Ti > 0.50 amphiboles need mended that the standard amphibole formula be special treatment, although it is recognised that calculated as follows, though it must be clearly Mn-rich amphiboles pose problems with the var­ appreciated that this is an arithmetic convention iable valency state of both the Fe and Mn and that, that assigns ions to convenient and reasonable site as shown by Hawthorne (1983, p. 183-5), both in occupancies. These cannot be confirmed without theory and practice, any calculation of Fe3 and Fe2 direct structural evidence. values is subject to considerable uncertainty. A

(1) If H2O and halogen contents are well estab­ full discussion of the problem and a recommended lished, the formula should be calculated to procedure, both by Dr J.C. Schumacher, are given 24(O,OH,F,Cl). as an appendix. Some analyses have H2O+ con­ (2) If the H2O and halogen content is uncertain, tents that lead to more than (OH)2 in the formula, the formula should be calculated to the basis but the structure contains only 2 sites for inde­ of 23(O) with 2(OH,F,Cl) assumed, unless this pendent OH" ions and the structural role of the ex­ leads to an impossibility of satisfying any of tra H ions is uncertain. the following criteria, in which case an appro­ The amphiboles are classified primarily into 4 priate change in the assumed number of groups depending on the occupancy of the B sites. (OH+F+Cl) should be made. These 4 principal amphibole groups are slightly (3) Sum T to 8.00 using Si, then Al, then Ti. For redefined as compared with IMA 78 and are: 3 the sake of simplicity of nomenclature Fe is (l)When (Ca+Na)B < 1.00 and L type ions not allocated to T. The normal maximum sub­ (Mg,Fe,Mn,Li)B > 1.00, then the amphibole is stitution for Si is 2, but this can be exceeded. a member of the magnesium-iron-manganese- (4) Sum C to 5.00 using excess Al and Ti from (3) lithium group. 3 3 3 and then successively Zr, Cr , Fe , Mn , Mg, (2) When (Ca+Na) > 1.00 and Na < 0.50, then 2 2 2 B B Fe , Mn , any other L type ions, and then Li. the amphibole is a member of the calcic 2 2 (5) Sum B to 2.00 using excess Mg, Fe , Mn and group. Usually, but not always, CaB > 1.50. Li from (4), then Ca, then Na. (3) When (Ca+Na)B > 1.00 and NaB 0.50 to 1.50, (6) Excess Na from (5) is assigned to A, then all then the amphibole is a member of the sodic- K. Total A should be between 0.00 and 1.00. calcic group. (4) When Na > 1.50, then the amphibole is a The most common uncertainty results from B 3 2 member of the sodic group, previously alkali lack of analyses for H2O, Fe and Fe . The pro­ 3 2 amphiboles. The new name is more precise, as cedure adopted to divide the Fe into Fe and Fe Na is the critical element, not any other alkali can influence the resulting name, especially if an element as K or Li. analysis is near to Mg/(Mg+Fe2) = 0.50 or Fe3/(Fe3+AlVI) = 0.50, i.e., the same analysis may Within each of these groups an analysis can give two or more names depending upon the allo­ then be named by reference to the appropriate cation of the Fe. The committee was almost un­ two-dimensional diagram (Fig. 2-5). These are animous in not wanting to specify one compulsory subdivided with respect to Si and Mg/(Mg+Fe2) or procedure for allocating Fe3 and Fe2 but in rec­ Mg/(Mg+Mn2), with prefixes to indicate major ommending that a common procedure be used for substitutions and optional modifiers to specify naming purposes. Rock & Leake (1984) showed less important substitutions. that, based on processing over 500 amphibole Within the groups, the amphiboles are divided analyses, the IMA-favoured procedure of adjust­ into individually named species distinguished ing the sum of the (Si+Al+Cr+Ti+Fe+Mg+Mn) to from one another on the basis of the heterovalent 3 2 IV 13 by varying the Fe and Fe appropriately gave substitutions: Si = A1 , D = (Na,K)A, CaB = NaB,

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2 2 Li = L , Mc = L C, (Ti,Zr) = Lc, O = (0H,F Cl). separately in the C group. The importance of the These substitutions necessarily occur in pairs or difference between R2 and R3 in the C group has, multiplets to maintain neutrality. The species de­ however, been recognised rather more formally fined on this basis are shown in Fig. l and along than previously by the way in which Fe3, Al3, Cr3 the horizontal axes of Fig. 2-5. Different species or Mn3 abundance has been defined with prefixes, defined in this way correspond to different distri­ not modifiers, when they occupy 50% or more of 3 butions of charge over the A, B, C, T, and "OH" the normal maximum of 2R C as shown in Table 1. sites. Discovery of amphiboles with new or quan­ Following Nickel & Mandarino (1988), pre­ titatively extended distributions of charge over fixes are an essential part of a mineral name (e.g., these sites would merit the introduction of new ferroglaucophane and ferro-actinolite), whereas species names. modifiers indicate a compositional variant, and Within the species there occur homovalent may be omitted (e.g., potassian pargasite). Mod­ substitutions, most commonly Mg = Fe2, AlVI = ifiers generally represent subsidiary substitutions Fe3 and OH = F. The end members of the substitu­ whereas prefixes denote major substitutions. In tion ranges are distinguished by the use of pre­ order to reduce the number of hyphens used, a fixes, one or other end member usually having a single prefix is generally joined directly to the traditional name without a prefix. These substi­ root name without a hyphen (e.g., ferrohornblen- tutions usually correspond to independent binary de) unless two vowels would then adjoin (e.g., systems X - - Y: the name of the X end member ferro-actinolite) or "an unhyphenated name is applies in the range l.00 > X/(X+Y) > 0.50 and awkward and a hyphen assists in deciphering the the name of the Y end member to 1.00 > Y/(X+Y) name" (Nickel & Mandarino, 1988) e.g. ferric- > 0.50. For the boundaries of substitution ranges nyboite. For all amphibole names involving multi­ in ternary systems see Nickel (1992). ple prefixes, a hyphen shall be inserted between The discovery of amphiboles with new or exo­ the prefixes but not between the last prefix and the tic homovalent substitutions never requires a new root name, unless two vowels would be juxta­ species name. They can always be named by use posed or the name would be difficult to decipher of an appropriate prefix. In future one root or triv­ or awkward. Thus alumino-ferrohornblende, ial name ONLY should be approved for each charge chloro-ferro-actinolite and fluoro-ferri-cannilloite. arrangement in each amphibole group and all species defined by homovalent substitutions should be designated by the relevant prefix. New species defined by heterovalent substitutions (in­ Table 1. Prefixes additional to those in the figures. cluding major oxygen replacement of (OH, F, Cl) and major entry of high (> 3) charged cations into Prefix Meaning Applicable to A, B or C) result in new root, or trivial names. The principal reference axes chosen for the Alumino A1A1> 1.00 Calcic & sodic-calcic calcic, sodic-calcic and sodic amphiboles are as in only Chloro Cl > 1.00 All groups IMA 78 namely Naß, (Na+K)A, and Si as shown in Fig. l, but the subdivision into the sodic-calcic Chromio Cr > 1.00 All groups Ferri Fe3 > 1.00 All groups except sodic group is now at Na 0.50 (instead of 0.67) and B Fluoro F > 1.00 All groups NaB l .50 (instead of l .34). This increases the vol­ Mangano Mn2 = 1.00-2.99 All groups except ume, and therefore the number of analyses, as­ kozulite & ungarettiite signed to the sodic-calcic amphiboles at the ex­ Permangano Mn2 = 3.00-4.99 All groups except kozulite pense of the calcic and sodic amphibole groups Mangani Mn3 > 1.00 All groups except kornite but is a logical consequence of applying the 50% & ungarettiite Potassic K > 0.50 All groups rule for all divisions rather than dividing the NaB, (Na+K) and Si box into equal volumes as in IMA Sodic Na > 0.50 Mg-Fe-Mn-Li only A Titano Ti > 0.50 All groups except kaer- 78. The committee considered at length various sutite proposals for the use of axes other than the three Zinco Zn > 1.00 All groups chosen, including four components, but eventually agreed, by a significant majority, that the IMA 78 The prefixes in the figures are ferro (Fe2 > Mg) and axes be retained, despite their inability to repre­ magnesio (Fe2 < Mg) and in Fig. 5a only ferric-nyboite sent R2 and R3 (i.e., usually L and M type ions) with A1IV < Fe3 (not ferricnyboite which is not clear).

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Table 2. Modifiers and their suggested ranges. Naming of amphiboles in thin section and hand specimen Modifier Meaning Applicable to For amphiboles of which the general nature only Barian Ba > 0.10 All groups is known, for instance from optical properties Borian B > 0.10 All groups without a chemical analysis, it is not generally Calcian Ca > 0.50 Mg-Fe-Mn-Li possible to allocate a precise name. The nearest Chlorian Cl = 0.25-0.99 All groups Chromian Cr = 0.25-0.99 All groups assigned amphibole name should then be made Ferrian Fe3 = 0.75-0.99 All groups except sodic into an adjective followed by the word amphibole. Fluorian F = 0.25-0.99 All groups Thus anthophyllitic amphibole, tremolitic amphi­ Hydroxylian OH > 3.00 All groups bole, pargasitic amphibole, glaucophanic amphi­ Lithian Li > 0.25 All groups but excludes bole and richteritic amphibole. The familiar word those defined by Li hornblende can still be used were appropriate for abundance (e.g. holm- calcic amphiboles in both hand specimen and thin quistite) 2 section, because hornblende is never used without Manganoan Mn = 0.25-0.99 All groups but excludes a ferro or magnesio prefix in the precise classifi­ those defined by Mn2 abundance cation, so no confusion should arise between col­ Manganian Mn3 or Mn4 = Ditto, Mn3 abundance loquial use and precise use. 0.25-0.99 (e.g. kornite) As in IMA 78, asbestiform amphiboles should Nickeloan Ni > 0.10 All groups be named according to their precise mineral name Oxygenian (OH+F+Cl)< 1.00 All groups except in this report, followed by the suffix-asbestos: ungarettiite e.g., anthophyllite-asbestos, tremolite-asbestos. Potass i an K = 0.25-0.49 All groups Where the nature of the mineral is uncertain or Plumbian Pb > 0.10 All groups unknown, asbestos alone or amphibole-asbestos Sodian Na = 0.25-0.49 Mg-Fe-Mn-Li only Strontian Sr > 0.10 All groups may be appropriate. If the approximate nature of Titanian Ti = 0.25-0.49 All groups the mineral only is known the above recommen­ Vanadian V > 0.10 All groups dations should be followed but the word amphi­ Zincian Zn > 0.10-0.99 All groups bole replaced by asbestos e.g. anthophyllitic as­ Zircon ian Zr > 0.10 All groups bestos, tremolitic asbestos.

Most (> 90%) names will lack any hyphens and Mg-Fe-Mn-Li amphiboles less than 5% will have more than one prefix. The group is defined as possessing (Ca+Na)B In general, excluding juxtaposed vowels, the < 1.00 and (Mg,Fe,Mn,Li)B > 1.00 in the standard prefixes (Table l), which have o, i or ic endings, formula; the detailed classification is shown in are either attached directly to the root name (with­ Fig. 2. The main changes from IMA 78 are the out a space or hyphen) or to a following prefix adoption of divisions at Mg/(Mg+Fe2) = 0.50, the with a hyphen. All these characters distinguish reduction of adjectives and the abolition of tirod- them from modifiers. ite and dannemorite. All the modifiers (Table 2) have 'ian' or 'oan' endings to indicate moderate substitutions as list­ ed by Nickel & Mandarino (1988). Modifiers are not accompanied by hyphens and are invariably Orthorhombic forms followed by a space and then the remainder of the name. The excluded applications follow from the (1) Anthophyllite series 2 fact that these groups will usually have substantial NaxLiz(Mg,Fe ,Mn)7_y_zAly(Si8_x.-y+zAl x+y_z)022 contents of these elements as part of the param­ (OH,F,C1)2 where Si > 7.00 (otherwise the mineral eters which define them. The use of modifiers is is gedrite) and Li < l .00 (otherwise the mineral is optional and strictly qualitative (i.e. they can be holmquistite). Most anthophyllites have the Pnma used in other senses than in Table 2 but use as in structure; those with the Pnmn structure may be Table 2 is strongly recommended). prefixed proto without a hyphen.

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Mg-Fe-Mn-Li amphiboles

2+ Diagram Parameters: (Ca + NaB) < 1.00; (Mg, Fe , Mn, Li)B > 1.00; LiB < 1.00 Orthorhombic Monoclinic

1.0Γ p w

anthophyllite gedrite cummingtonite

UL

™O) 0.5 k

ferro- ferrogedrite anthophyllite grunerite

0.0 L L _L _L L J 8.0 7.0 6.0 8.0 7.0 Si in formula Si in formula

2+ Diagram Parameters.(C a + NaB) < 1.00; (Mg, Fe , Mn, Li)B >1.00; LiB> 1.00 Orthorhombic I Monoclinic

1.ÖΓF

holmquistite clinoholmquistite

Final names require the relevent prefixes which are listed in ™U) 0.5 Table 1 and may optionally include the modifiers that are found in Table 2. clinoferroholmquistite ferroholmqujstite w w % ' symbols indicate the locations of end u A. M member formulae 0.0 t^_ listed in the text. 8.0 7.0 8.0 7.0 Si in formula Si in formula

Fig. 2. Classification of the Mg-Fe-Mn-Li amphiboles.

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End members Anthophyllite DMg7Si8O22(OH)2 Ferro-anthophyllite DFe?Si8O22(OH)2 Sodicanthophyllite NaMg7Si7AlO22(OH)2 Sodic-ferro-anthophyllite NaFe?Si7AlO22(OH)2 Limits for the use of end member names Anthophyllite Mg/(Mg+Fe2) > 0.50 Ferro-anthophyllite Mg/(Mg+Fe2) < 0.50 Sodicanthophyllite Mg/(Mg+Fe2) > 0.50; Na > 0.50 Sodic-ferro-anthophyllite Mg/(Mg+Fe2) < 0.50; Na > 0.50

(2) Gedrite series

2 NaxLiz(Mg,Fe ,Mn)7_y_zAly(Si8_x_y+Alx+y-z)022(OH,F,Cl)2 where x+y-z > 1.00 so that Si < 7.00 this being the distinction from anthophyllite. Li< 1.00.

End members Gedrite D Mg5Al2Si6Al2O22(OH)2 Ferrogedrite DFeiAl2Si6Al2O22(OH)2 Sodicgedrite NaMg6AlSi6Al2O22(OH)2 Sodic-ferrogedrite NaFe^AlSi6Al2O22(OH)2 Limits for the use of end member names Gedrite Mg/(Mg+Fe2) > 0.50 Ferrogedrite Mg/(Mg+Fe2) < 0.50 Sodicgedrite Mg/(Mg+Fe2) > 0.50; Na > 0.50 Sodic-ferrogedrite Mg/(Mg+Fe2) < 0.50; Na > 0.50 It should be noted that gedrite and ferrogedrite, with or without sodic prefixes, extend down to at least Si 5.50. Discovery of homogeneous Na(Fe,Mg)5Al2Si5Al3O22(OH)2 will justify a new name.

(3) Holmquistite series

2 3 DLi2(Mg,Fe )3(Fe ,Al)2Si8O22(OH,F,Cl)2. Li > 1.00 is critical.

End members Holmquistite D (Li2Mg3Al2)Si8O22(OH)2 Ferroholmquistite D (Li2Fe32Al2)Si8O22(OH)2 Limits for the use of end member names Holmquistite Mg/(Mg+Fe2) > 0.50 Ferroholmquistite Mg/(Mg+Fe2) < 0.50

Monoclinic forms (1) Cummingtonite-Grunerite series 2 D (Mg,Fe ,Mn,Li)7Si8O22(OH)2. Li < 1.00. Most members of this series have space group C2/m; those with P2/m may optionally have this symbol suffixed at the end of the name.

End members Cummingtonite DMg7Si8O22(OH)2 Grunerite DFe2Si8O22(OH)2

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calcic amphiboles

Diagram Parameters: CaB > 1.50; (Na + K)A > 0.50 Ti < 0.50 Ti > 0.50

1.0r m w w 1 pargasite (A|Vi>Fe3+) edenite magnesiosadanagaite kaersutite magnesiohastingsite LL (Aivi < Fe3+)

Ö) 0.5 ferropargasite O) (Aivi > 3+) ferro-edenite Fe sadanagaite ferrokaersutite hastingsite (Aivi < Fe3+) 0.0' ä- ÉÉÉ •

Diagram Parameters: (CaB > 1.50; (Na + K)A < 0.50)

CaA < 0.50 CaA > 0.50

1.0 W I j tremoHte 0.9 cannilloite actinolite magnesjohornblende tschermakite

CD Final names require the relevent prefixes which are listed in O) 0.5 Table 1 and may optionally include the modifiers that are ferro- found in Table 2. ferrotschermakite . actinolite ferrohomblende symbols indicate the locations of end member formulae 0.0 li & m I listed in the text. 8.0 7.5 7.0 6.5 6.0 5.5 Si in formula

Fig. 3. Classification of the calcic amphiboles.

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Calcic amphiboles have been revised. Hornblende is retained as a general or colloquial term for coloured calcic am­ The group is defined as monoclinic amphiboles in phiboles without confusion with the precise range which (Ca+Na)B > 1.00 and NaB = 0.50 to 1.50; shown in Fig. 3 because hornblende is always usually CaB > 1.50. The detailed classification is pre-fixed with ferro or magnesio in the precise shown in Fig. 3. The number of subdivisions used nomenclature. Because of the strong desire in IMA 78 has been more than halved; silicic ede- especially, but not solely by metamorphic petrol- nite and compound names like tschermakitic ogists, to retain the distinction of green actinolite hornblende have been abolished, sadanagaite, from colourless tremolite, the subdivisions trem­ which was approved in 1984 (Shimazaki et ah, olite, actinolite, ferro-actinolite of IMA 78 are re­ 1984), and cannilloite (Hawthorne et ai, 1996), tained as shown in Fig. 3. have been added, and the boundaries of the group

End members Tremolite DCa2Mg5Si8O22(OH)2 Ferro-actinolite DCa2FeiSi8O22(OH)2 Edenite NaCa2Mg5Si7AlO22(OH)2 Ferro-edenite NaCa2FeiSi7AlO22(OH)2 Pargasite NaCa2(Mg4Al)Si6Al2O22(OH)2 Ferropargasite NaCa2(FejAl)Si6Al2O22(OH)2 3 Magnesiohastingsite NaCa2(Mg4Fe )Si6Al2O22(OH)2 3 Hastingsite NaCa2(Fe^Fe )Si6Al2O22(OH)2 3 Tschermakite D Ca2(Mg3AlFe )Si6Al2O22(OH)2 3 Ferrotschermakite D Ca2(Fei AlFe )Si6Al2O22(OH)2 Aluminotschermakite D Ca2(Mg3Al2)Si6Al2O22(OH)2 Aluminoferrotschermakite D Ca2(Fe! Al2)Si6Al2O22(OH)2 5 Ferritschermakite D Ca2(Mg3Fe2 )Si6Al2O22(OH)2 Ferri-ferrotschermakite D Ca2(Fe^Fe^)Si6Al2O22(OH)2 3 Magnesiosadanagaite NaCa2(Mg3(Fe ,Al)2)Si5Al3O22(OH)2 3 Sadanagaite NaCa2(Fe^(Fe ,Al)2)Si5Al3O22(OH)2 3 Magnesiohornblende D Ca2(Mg4(Al,Fe ))Si7AlO22(OH)2 3 Ferrohornblende D Ca2(Fe5(Al,Fe ))Si7AlO22(OH)2 Kaersutite NaCa2(Mg4Ti)Si6Al2O23(OH) Ferrokaersutite NaCa2(FelTi)Si6Al2O23(OH) Cannilloite CaCa2(Mg4Al)Si5Al3O22(OH)2

Limits for the use of the end member names A1VI > 1.00 (Table 1). For kaersutite and ferro­ These are summarised in Fig. 3 with respect to Si, kaersutite, Ti > 0.50; any lesser Ti content may 2 (Na+K)A, Mg/(Mg+Fe ) and Ti. The prefixes ferri optionally be indicated as in Table 2. Cannilloite 3 and alumino are only used when Fe > 1.00 and requires CaA > 0.50.

Sodic-calcic amphiboles centration of analyses relatively near to the end member compositions, the increase in the number This group is defined as monoclinic amphiboles of analyses in this group compared with the num­ in which (Ca+Na)B > 1.00 and 0.50 < NaB < 1.50. ber classified in IMA 78 is quite small (much less The detailed classification is shown in Fig. 4. than 50%). Nevertheless a number of previously There are no significant changes from IMA 78 classified calcic and alkali amphiboles now be­ except for the 50% expansion of the volume oc­ come sodic-calcic amphiboles. cupied in Fig. 1 by the group. Because of the con-

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sodic-calcic amphiboles

Diagram Parameters:

(Na + K)A > 0.50; (Ca + NaB) > 1.00; 0.50 < NaB < 1.50

1.0r f | w IP 1

richterite magnesiokatophorite magnesiotaramite + CMα > LL

O) 0.5 h

O) ferro katophorite taramite richterite

0.0 LL* L 8.0 7.5 70 6.5 60 5.5 Si in formula

Diagram Parameters:

(Na + K)A < 0.50; (Ca + NaB) > 1.00; 0.50 < NaB < 1.50

1.0rrw I m 1

winchite barroisite + CM

Fig. 4. Classification of the sodic-calcic amphiboles.

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End members Richerite Na(CaNa)Mg5Si8O22(OH)2 Ferrorichterite Na(CaNa)Fe^Si8O22(OH)2 3 Winchite D (CaNa)Mg4(Al,Fe )Si8O22(OH)2 3 Ferrowinchite D (CaNa)FeJ(Al,Fe )Si8022(0H)2 3 Barroisite D (CaNa)Mg3AlFe Si7AlO22(OH)2 3 Ferrobarroisite D (CaNa)Fe^AlFe Si7A1022(0H)2 Aluminobarroisite D (CaNa)Mg3Al2Si7AlO22(OH)2 Alumino-ferrobarroisite D (CaNa)Fe^Al2Si7A1022(0H)2 Ferribarroisite D (CaNa)Mg3Fe^Si7AlO22(OH)2 Ferri-ferrobarroisite D (CaNa)Fe^Fe^Si7AlO22(OH)2 3 Magnesiokatophorite Na(CaNa)Mg4(Al,Fe )Si7AlO22(OH)2 3 Katophorite Na(CaNa)Fe^(Al,Fe )Si7AlO22(OH)2 3 Magnesiotaramite Na(CaNa)Mg3AlFe Si6Al2O22(OH)2 3 Taramite Na(CaNa)Fe|AlFe Si6Al2022(0H)2 Alumino-magnesiotaramite Na(CaNa)Mg3Al2Si6Al2O22(OH)2 Aluminotaramite Na(CaNa)Fe^Al2Si6Al2O22(OH)2~ Ferri-magnesiotaramite Na(CaNa)Mg3Fe^Si6Al2O22(OH)2 Ferritaramite Na(CaNa)Fe^Fe^Si6Al2O22(OH)2

Limits for the use of end member names again restricted to A1V1 > 1.00 and Fe3 > l.00 These are summarised in Fig. 4 with respect to Si, being 50% of the normal maximum of 2Rc3 2 (Na+K)A and Mg/(Mg+Fe ). Alumino and ferri are places.

Sodic amphiboles lowed, the principal changes are the introduction of nyboite with Si close to 7, as approved in 1981 This group is defined as monoclinic amphiboles (Ungaretti et al, 1981), ferric-nyboite (instead of in which NaB > l .50. The detailed classification is anophorite), leakeite (Hawthorne et al, 1992), shown in Fig. 5. Apart from revision of the bound­ ferroleakeite (Hawthorne et al, 1996), kornite ary NaB > 1.50 instead of NaB > 1.34, and the abo­ (Armbruster et al, 1993), and ungarettiite lition of crossite so that the 50% division is fol- (Hawthorne et al, 1995).

End members Glaucophane D Na2(Mg3Al2)Si8O22(OH)2 Ferroglaucophane D Na2(Fe5Al2)Si8O22(OH)2 Magnesioriebeckite D Na2(Mg3Fe^)Si8O22(OH)2 Riebeckite D Na2(Fe5Fe^)Si8O22(OH)2 Eckermannite NaNa2(Mg4Al)Si8O2"2(OHJ2 Ferro-eckermannite NaNa2(Fe^Al)Si8O22(OH)2 3 Magnesio-arfvedsonite NaNa2(Mg4Fe )Si8O22(OH)2 3 Arfvedsonite NaNa2(Fe^Fe )Si8O22(OH)2 3 Kozulite NaNa2(MnJ(Fe ,Al))Si8O22(OH)2 Nyboite NaNa2(Mg3Al2)Si7AlO22(OH)2 Ferronyboite NaNa2(Fe^Al2)Si7AlO22(OH)2~ Ferric-nyboite NaNa2(Mg3Fe^)Si7AlO22(OH)2 Ferric-ferronyboite NaNa2(Fe?Fe5)Si7AlO22(OH)2^ Leakeite NaNa2(Mg2Fe^Li)Si8O22(OH)2 Ferroleakeite NaNa2(Fe?Fe^Li)Si8O22(OH)2" Kornite (Na,K)Na2(Mg2Mn^Li)Si8O22(OH)2 Ungarettiite NaNa2(Mn^Mn^)Si8O22O2

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2+ 2+ 2+ 2+ Diagram Parameters: NaB > 1.50; (Mg + Fe + Mn ) > 2.5; Diagram Parameters: NaB > 1.50; (Mg + Fe + Mn ) > 2.5;

(Alvl or Fe3+) > Mn3+; Li < 0.5; (Mg or Fe2+) > Mn2+ (AIVI or Fe3+) > Mn3+; Li < 0.5; (Mg or Mn2+) > Fe2+

(Na + K)A < 0.50 (Na + K)A > 0.50 (Na + K)A > 0.50

1.0 1.0Γ m | 1.0 p glaucophane eckermannite nyboite eckermannite (A|Vi>Fe3+) (A|Vl>Fe3+) \ (A|Vi>Fβ3+) (A|Vl>Fe3^)

magnesio- magnesio- + magnesioriebeckite + arfvedsonite + arfvedsonite ferric-nyboite CM CM (A|Vi0.5 I eckermannite ferronyboite ferroglaucophane (A|Vi> 3 ) (A|Vi>Fe3+) Fe + (A|VI>Fe3+) 5 kozulite

riebeckite arfvedsonite ferric-ferronyboite (A|Vl

Fig. 5a. Classification of the sodic amphiboles with (Mg+Fe2+Mn2) > 2.5.

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sodic amphiboles

2+ 2+ Diagram Parameters: NaB > 1.50; (Na + K)A > 0.50; (Mg + Fe + Mn ) < 2.5; Li > 0.5 (Mg or Fe2+) > Mn2+ (Mg or Mn2+) > Fe2+

1.0Γ p 1.0ΓFp leakeite leakeite (Fe3+> [AIVI or Mn3+]) (Fe3+>[A|ViorMn3+]) ω CM + c 0.5 + 0.5 O) D) ferroleakeite kornite (Fe3+>[AlorMn3+]) (Mn3+>[AlvlorFe3+])

0.0 Llà 0.0 L k 8.0 7.5 7.0 8.0 7.5 7.0 Si in formula Si in formula

2+ 2+ Diagram Parameters: NaB > 1.50; (Na + K)A > 0.50; (Mg + Fe + Mn ) < 2.5; Li < 0.5 (Mg or Mn2+) > Fe2+

1.0

Final names require the relevent prefixes which are listed in S)0.5h Table 1 and may optionally include the modifiers that are found in Table 2. O) 1 2 ungarettiite % : symbols indicate (Mn3+>[A|Vi0rFe3+]) the locations of end member formulae listed in the text. 0.0 LHli J_ 8.0 7.5 7.0 Si in formula

tideal formula is free of OH,F,CI; the anion configuration is: ...O22 O2

Fig. 5b. Classification of the sodic amphiboles with (Mg+Fe2+Mn2) < 2.5.

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Limits for the use of end member names require Mg/(Mg+Fe2) > 0.50, Li > 0.50 with Fe3 > These are summarised in Fig. 5 with respect to Si, Mn3 in leakeite and Fe3 < Mn3 in kornite. Ferric- 2 3 VI (Na+K)A and Mg/(Mg+Fe ), Li and Mn param- nyboite means Fe > Al and should be clearly eters. Kozulite requires Mn2 > Fe2+Fe3+Mg+Alvl distinguished from ferri (meaning Fe3 > 1.00) with AlVI or Fe3 > Mn3,Li < 0.5; ungarettiite has becaus^^"^e neithen^th^rr aluminαi,,™.™o (meanin/s^αr..™g AΛIVl I 1.00) both Mn2 and Mn3 > Fe2+Mg+Fe3+AlVI with Li < nor ferri are used in the sodic amphiboles. 0.50 and (OH+F+Cl) < 1.00; leakeite and kornite

Amphibole names recommended for extinction The following amphibole names used in IMA 78 are recommended to be formally abandoned. IMA 78 lists 193 abandoned names. Magnesio-anthophyllite anthophyllite Sodium-anthophyllite sodicanthophyllite Magnesio-gedrite gedrite Sodium gedrite sodicgedrite Magnesio-holmquistite holmquistite Magnesio-cummingtonite cummingtonite Tirodite manganocummingtonite Dannemorite manganogrunerite Magnesio-clinoholmquistite clinoholmquistite Crossite glaucophane or ferroglaucophane or magnesioriebeckite or riebeckite Tremolitic hornblende = magnesiohornblende Actinolitic hornblende = magnesiohornblende Ferro-actinolitic hornblende = ferrohornblende Tschermakitic hornblende = tschermakite Ferro-tschermakitic hornblende = ferrotschermakite Edenitic hornblende = edenite Ferro-edenitic hornblende = ferro-edenite Pargasitic hornblende = pargasite Ferroan pargasitic = pargasite or ferrohornblendepargasite Ferro-pargasitic hornblende = ferropargasite Ferroan pargasite = pargasite or ferropargasite Silicic edenite = edenite Silicic ferro-edenite = ferro-edenite Magnesio-hastingsitic hornblende = magnesiohastingsite Magnesian hastingsitic hornblende = magnesiohastingsite or hastingsite Hastingsitic hornblende = hastingsite Magnesian hastingsite = magnesiohastingsite or hastingsite

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References Hawthorne, F.C, Oberti, R., Ungaretti, L., Ottolini, L„ Grice, J.D., Czamanske, G.K. (1996): Fluor-ferro- + + Anthony, J.W., Bideaux, R.A., Bladh, K.W., Nichols, leakeite, NaNa2(Fe^ Fe^ Li)Si8O22F2, a new alkali M.C. (1995): Handbook of Mineralogy, 2, pt. 1. amphibole from the Canada Pinabete pluton, Que- Mineral Data Publishing, Tucson, Arizona. 446 pp. sta, New Mexico, U.S.A. Amer. Mineral, 81, 226 Armbruster, T., Oberhänsli, R., Bermanec, V., Dixon, R. -228. 3+ (1993): Hennomartinite and kornite, two new Mn IMA (1978): Nomenclature of amphiboles. Mineral rich silicates from the Wessels Mine, Kalahari, Mag., 42, 533-563. South Africa. Schweiz. Mineral. Petrogr. Mitt., 73, Nambu, M., Tanida, K., Kitamura, T. (1969): Kozulite, a 349-355. new alkali amphibole from Tanohata Mine, Iwate Chukhrov, F.V. (Ed.) (1981): Minerals: a handbook. 3, Prefecture, Japan. /. Japan. Assoc. Mineral, Petrol. pt. 3. Silicates with multiple chains of Si-0 tetrahe- Econ. Geol, 62, 311-328. dra. Nauka, Moscow. 397 pp. Nickel, E.H. (1992): Nomenclature for mineral solid so­ Deer, W.A., Howie, R.A., Zussman, J. (1963): Rock- lutions. Amer. Mineral, 11, 660- 662. forming Minerals, 2, Chain silicates. Longmans, Nickel, E.H. & Mandarino, J.A. (1988): Procedures in­ London. 379 pp. volving the IMA Commission on New Minerals and (1997): Rock-forming Minerals 2B, Double-Chain Mineral Names, and guidelines on mineral nomen­ Silicates. Geol. Soc. London (in press). clature. Mineral. Mag., 52, 275-292. Ernst, W.G. (1968): Amphiboles. Springer-Verlag, New Rock, N.M.S. & Leake, B.E. (1984): The International York. 119 pp. Mineralogical Association amphibole nomenclature Hawthorne, F.C. (1983): The crystal chemistry of the scheme: computerization and its consequences. amphiboles. Canad. Mineral, 21, 173-480. Mineral. Mag., 48, 211-217. Hawthorne, F.C, Oberti, R., Cannillo, E., Sardonne, N., Shimazaki, H., Bunno, M., Ozawa, T. (1984): Sadan- Zanetti, A., Grice, J.D., Ashley, P.M. (1995): Anew agaite and magnesio-sadanagaite, new silica-poor anhydrous amphibole from the Hoskins mine, members of calcic amphibole from Japan. Amer. Grenfell, New South Wales, Australia: Descrip­ Mineral, 69, 465-471. tion and crystal structure of ungarettiite, Ungaretti, L., Smith, D.C, Rossi, G. (1981): Crystal- + NaNa2(Mn5 Mn^)Si8O22O2- Amer. Mineral, 80, chemistry by X-ray structure refinement and 165-172. electron microprobe analysis of a series of sodic- Hawthorne, F.C, Oberti, R., Ungaretti, L., Grice, J.D. calcic to alkali amphiboles from the Nybo eclogite (1992): Leakeite, NaNa2(Mg2Fe^Li)Si8O22(OH)2, pod, Norway. Bull Mineral, 104, 400-412. a new alkali amphibole from the Kajlidongri man­ Veblen, D.R. (Ed.) (1981): Amphiboles and other hy­ ganese mine, Jhabua district, Madhya Pradesh, In­ drous pyriboles - mineralogy. Reviews in Mineral­ dia. Amer. Mineral, 77, 1112-1115. ogy, 9A. Mineral. Soc. Amer. 372 pp. (1996): A new hyper-calcic amphibole with Ca at Veblen, D.R. & Ribbe, PH. (Eds.) (1982): Amphiboles: the A site: fluor-cannilloite from Pargas, Finland. petrology and experimental phase relations. Re­ Amer. Mineral, 81, 995-1002. views in Mineralogy, 9B. Mineral. Soc. Amer. 390 pp.

APPENDIX 1 Amphibole end-members

Actinolite. Named from the Greek aktin a ray and Anthophyllite. Named from anthophyllum 'clove' lithos a stone, alluding to the radiating habit. referring to its characteristic brown colour. Type locality: None Type locality: Described by Schumacher (1801, p. X-ray data: a 9.884 Å, b 18.145 Å, c 5.294 Å. ß 96) as from the Kongsberg area, Norway, the ex­ 104.7°. act locality being kept secret, but later (Moller, (PDF 25-157 on specimen from Sobotin, Czech 1825) as from the Kjennerudvann Lake near Republic) Kongsberg. References: R. Kirwan (1794. Elements of Min­ X-ray data: a 18.5 Å, b 17.9 Å, c 5.28 Å. eralogy, 1: 167) (actynolite): modified by J.D. (PDF 9-455 on specimen from Georgia, USA) Dana (1837. Syst. Min. 1st ed., 309). References: N.B. Moller (1825. Magazin for Na- turvedenskaberne. Christiania, 6: 174). C.F. Schu­ macher (1801. Versuch Verzeich. Danisch-Nor- disch Staat, einfach Min. 96 and 165).

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Arfvedsonite. Named for J.A. Arfvedson. References: O.J. Adamson (1942. Geol. For. Type locality: Kangerdluarsuk, Greenland. Stockh., 64: 329; ibid. 1944. 66: 194). Defined by X-ray data: a 9.94 Å, b 18.17 Å, c 5.34 Å. ß B.E. Leake (1978. Min. Mag., 42: 546). 104.40°. (PDF 14-633 on specimen from Nunarsuatsiak, Edenite. Named for locality. Greenland) Type locality: Eden (Edenvilie), New York, USA. References: H.J. Brooke (1823. Ann. Phil, 21: X-ray data: a 9.837 Å, b 17.954 Å, c 5.307 Å. ß (2nd sen, vol. 5) 381) (arfwedsonite): amended by 105.18°. T. Thomson (1836. Outlines of Mineralogy, Geol­ (PDF 23-1405 on specimen from Franklin Fur­ ogy, and Mineral Analysis, 1: 483). nace, New Jersey, USA) References: Not analysed in original description. Barroisite. Origin of name not found. Two analyses of topotype material by C.F. Ram- Type locality: Not traced. melsberg (1858. Ann. Phys. Chem. (Pogg), 103: References: G. Murgoci (1922. C.R. Acad. Sci. 441) and G.W. Hawes (1878. Amer. J. Sci., Ser. 3, Paris, 175A: 373 and 426). Now defined by B.E. 16: 397) differ considerably, and neither falls with­ Leake (1978. Min. Mag., 42: 544). in edenite range of Leake (1978. Min. Mag., 42: 542). Current definition proposed by N. Sundius Cannilloite. Named for Elio Cannillo of Pavia, (1946. Årsb. Sver. Geol. Unders., 40: no. 4). Near­ Italy. est analysis to end-member may be that of Leake Type locality: Pargas, Finland. (1971. Min. Mag., 38: 405). X-ray data: (Fluor-cannilloite) a 9.826 Å, b 17.907 Å,c 5.301 Å, ß 105.41°. Gedrite. Named from locality. Reference: EC. Hawthorne, R. Oberti, L. Unga- Type locality: Héas Valley, near Gèdres, France. retti & J.D. Grice (1996. Am. Min., 81: 995). X-ray data: a 18.594 Å, b 17.890 Å, c 5.304 Å. (PDF 13-506 on specimen from Grafton, Oxford Clinoholmquistite. Named as a monoclinic poly- County, Maine, USA) morph of holmquistite. References: A Dufrenoy (1836. Ann. Mines, ser. 3, Type locality: Golzy, Sayany Mountain, Siberia, 10: 582). Defined by B.E. Leake (1978. Min. Russia. Mag., 42: 539). X-ray data: a 9.80 Å, b 17.83 Å, c 5.30 Å. ß 109.10°. Glaucophane. Named from the Greek glaukos, (PDF 25-498 on specimen from Siberia, Russia) bluish green and phainesthai, to appear. References: I.V. Ginzburg (1965. Trudy Min. Muz. Type locality: Syra, Cyclades, Greece. Akad. Nauk. SSSR, 16: 73). In B.E. Leake (1978. X-ray data: a 9.595 Å, b 17.798 Å, c 5.307 Å. ß Min. Mag., 42: 540) defined in a series with 103.66°. magnesio-clinoholmquistite and ferro-clino- (PDF 20-453 on specimen from Sebastopol Quad­ holmquistite. rangle, California, USA. See also PDF 15-58 and 20-616) Cummingtonite. Named for locality. Reference: J.F.L. Hausman (1845. Gel. Kon. Ges. Type locality: Cummington, Ma., USA. Wiss. Gottingen, p. 125) (Glaukophan). X-ray data: a 9.534 Å, b 18.231 Å, c 5.3235 Å. ß 101.97°. Grunerite. Named for E.L. Gruner. (PDF 31 -636 on specimen from Wabush iron for­ Type locality: Collobrières, Var, France. mation, Labrador, Canada) X-ray data: a 9.57 Å, b 18.22 Å, c 5.33 Å. References: C. Dewey (1824. Amer. J. Sci., ser. 1, (PDF 17-745 on specimen from White Lake, Lab­ 8: 58). Defined by B.E. Leake (1978. Min. Mag., rador, Canada) 42: 549). References: Described by E.L. Gruner (1847. C.R. Acad. Sci. Paris, 24: 794) but named by A. Kenn- Eckermannite. Named for H. von Eckermann. gott (1853. Mohs'sche Min. Syst., 69). Defined by Type locality: Norra Kärr, Sweden. B.E. Leake (1978. Min. Mag., 42: 549). X-ray data: a 9.7652 Å, b 17.892 Å, c 5.284 Å. ß 103.168°. Hastingsite. Named for locality. (PDF 20-386 on synthetic material) Type locality: Hastings County, Ontario, Canada.

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X-ray data: a 9.907 Å, b 18.023 Å, c 5.278 Å. ß Reference: T Armbruster, R. Oberhänsli, V. Ber- 105.058°. manec & R. Dixon (1993. Schweiz. Mineral. Pe- (PDF 20-378 on specimen from Dashkesan, Trans­ trogr. Mitt., 73: 349). caucasia, Russia. Also PDF 20-469) References: F.D. Adams & B.J. Harrington (1896. Kozulite. Named for S. Kozu. Amer. J. ScL, 4th sen, 1: 212; 1896. Canad. Rec. Type locality: Tanohata mine, Iwate Prefecture, ScL, 7: 81). Defined by B.E. Leake (1978. Min. Japan. Mag., 42: 553). X-ray data: a 9.991 Å, b 18.11 Å, c 5.30 Å. ß 104.6°. Holmquistite. Named for P.J. Holmquist. (PDF 25-850) Type locality: Uto, Stockholm, Sweden. References: M. Nambu, K. Tanida & T. Kitamura X-ray data: a 18.30 Å, b 17.69 Å, c 5.30 Å. (1969. J. Japan. Assoc. Min. Petr. Econ. Geol, 62: (PDF 13-401 on specimen from Barrante, Quebec, 311). Defined by B.E. Leake (1978. Min. Mag., Canada) 42: 557). References: A. Osann (1913. Sitz. Heidelberg Akad. Wiss., Abt. A, Abh., 23). Dimorphous with Leakeite. Named for B.E. Leake. clinoholmquistite. Defined by B.E. Leake (1978. Type locality: Kajlidongri manganese mine, Jha- Min. Mag., 42: 549). bua district, Madhya Pradesh, India. X-ray data: a 9.822 Å, b 17.836 Å, c 5.286 Å. ß Hornblende. The name is from the German min­ 104.37°. ing term horn, horn, and blenden, to dazzle. Reference: F.C. Hawthorne, R. Oberti, L. Unga- Reference: Use of the term hornblende and rela­ retti & J.D. Grice (1992. Am. Min., 77: 1112). tionship to other calcic amphiboles discussed by Deer et al. (1963. Rock-forming minerals. 2. Nyboite. Named from locality. Chain silicates. 265. Longmans, London), defined Type locality: Nybo, Nordfjord, Norway. by B.E. Leake (1978. Min. Mag., 42: 551). X-ray data: In Ungaretti et al. (1981) X-ray data given for many specimens and a single 'type' Kaersutite. Named from locality. specimen not distinguished. Type locality: Kaersut, Umanaksfjord, Greenland. Reference: L. Ungaretti, D.C. Smith & G. Rossi X-ray data: a 9.83 Å, b 17.89 Å, c 5.30 Å. ß (1981. Bw//. Min., 104:400). 105.18°. (PDF 17-478 on specimen from Boulder Dam, Pargasite. Named from locality. Arizona, USA) Type locality: Pargas, Finland. References: J. Lorenzen (1884. Medd. Gr0nland, X-ray data: a 9.870 Å, b 18.006 Å, c 5.300 Å. ß 7: 27). Defined and given species status by B.E. 105.43°. Leake (1978. Min. Mag., 42: 551). (PDF 23-1406 and PDF 41-1430 on synthetic ma­ terial) Katophorite. Named from the Greek kataphora a References: F. von Steinheil (1814 in Tasch. Min. rushing down, in reference to its volcanic origin. (1815) Jahrg. 9, Abt. 1, 309). The name was wide­ Type locality: Christiana District (now Oslo), ly used for green hornblende but was redefined by Norway. N. Sundius (1946. Arsb. Sver. Geol. Undersk., 40: References: W.C. Brogger (1894. Die Eruptivgest. 18) and B.E. Leake (1978. Min. Mag., 42: 550 and Kristianiagebietes, Skr. Vid.-Selsk I. Math.-natur. 552). Kl. 4: 27). Frequently termed catophorite, and other variants, but accepted IMA spelling is kato­ Richterite. Named for T. Richter. phorite. Defined by B.E. Leake (1978. Min. Mag., Type locality: Làngban, Värmland, Sweden. 42: 544). X-ray data: a 9.907 Å, b 17.979 Å, c 5.269 Å. ß 104.25°. Kornite. Named for H. Korn. (PDF 254-808 on synthetic material; see also PDF Type locality: Wessels Mine, Kalahari Manganese 31-1284 for calcian and 25-675 and 31-1082 for Fields, South Africa. potassian) X-ray data: a 9.94(1) Å, b 17.80(2) Å, c 5.302(4) References: An imperfect description by A. Breit- Å. ß 105.52°. haupt (1865. Bergmann Huttenmann. Zeit., 24:

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364) was shown by H. Sjogren (1895. Bull. Geol. Tschermakite. Named for G. Tschermak. Origi­ Inst. Univ. Upsala, 2: 71) to be an amphibole. De­ nally described as a hypothetical 'Tschermak fined by B.E. Leake (1978. Min. Mag., 42: 544). molecule'. References: A.N. Winchell (1945. Amer. Min., 30: Riebeckite. Named for E. Riebeck. 29). Defined by B.E. Leake (1978. Min. Mag., 42: Type locality: Island of Socotra, Indian Ocean. 550 and 552). X-ray data: a 9.769 Å, b 18.048 Å, c 5.335 Å. ß 103.59°. Ungarettiite. Named for L. Ungaretti. (PDF 19-1061 on specimen from Doubrutscha, Type locality: Hoskins mine, near Grenfell, New Romania) South Wales, Australia. References: A. Sauer (1888, Zeit. deutsch. geol X-ray data: a 9.89(2) Å, b 18.04(3) Å, c 5.29(1) Ges., 40: 138). Defined by B.E. Leake (1978. Å. ß 104.6(2)°. Min. Mag., 42: 546). Reference: F.C. Hawthorne, R. Oberti, E. Cannil- lo, N. Sardone & A. Zanetti (1995. Amer. Min., Sadanagaite. Named for R. Sadanaga. 80: 165). Type locality: Yuge and Myojin Islands, Japan. X-ray data: a 9.922 Å, b 18.03 Å, c 5.352 Å. ß Winchite. Named for H.J. Winch, who found the 105.30°. amphibole. Reference: H. Shimazaki, M. Bunno & T. Ozawa Type locality: Kajlidongri, Jhabua State, India. (1984. Amer. Min., 89:465). X-ray data: a 9.834 Å, b 18.062 Å, c 5.300 Å. ß 104.4°. Taramite. Named from type locality. (PDF 20-1390) Type locality: Walitarama, Mariupol, Ukraine. References: L.L. Fermor (1906. Trans. Mining X-ray data: a 9.952 Å, b 18.101 Å, c 5.322 Å. ß Geol. Inst. India, 1: 79) naming the amphibole de­ 105.45°. scribed in 1904 (Rec. Geol. Surv. India, 31: 236). (PDF 20-734 on specimen of potassian taramite Topotype material found by B.E. Leake, CM. from Mbozi complex, Tanzania) Farrow, F. Chao & V.K. Nayak (1986. Min. Mag., References: J. Morozewicz (1923. Spraw. Polsk. 50: 174) proved to be very similar in composition Inst. Geol (Bull. Serv. Geol. Pologne), 2: 6). Rede­ to that originally found by Fermor (1909. Mem. fined by Leake (1978. Min. Mag., 42: 544). Geol Surv. India, 37: 149).

Tremolite. Named from locality. General references Type locality: Val Tremola, St. Gotthard, Switzer­ land. Chukhrov, F.V. (Ed.) (1981): Minerals: a handbook. Vol. X-ray data: a 9.84 Å, b 18.02 Å, c 5.27 Å. ß 3, pt. 3. Silicates with multiple chains of Si-0 tetra- 104.95°. hedra. Nauka, Moscow. 397 pp. (PDF 13-437 on specimen from San Gottardo, Clark, A.M. (1993): Hey's mineral index. Natural His­ tory Museum and Chapman & Hall, London. 852 Switzerland and PDF 31-1285 on synthetic mate­ pp. rial) Deer, W.A., Howie, R.A., Zussman, J. (1963): Rock- References: E. Pini (1796. In H.-B. Saussure, forming minerals. Vol. 2. Chain silicates. 203-374. 1923. Voyages dans les Alpes, 4: sect). Defined by Longmans, London. B.E. Leake (1978. Min. Mag., 42: 542). Leake, B.E. (1978): Nomenclature of amphiboles. Min­ eral Mag., 42, 533-563.

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APPENDIX 2

The estimation of ferric iron in electron microprobe analysis of amphiboles

JOHN C. SCHUMACHER

Institut fur Mineralogie-Petrologie-Geochemie, Universität Freiburg, D-79104 Freiburg i.Br., Germany

Introduction until it is possible to determine ferric contents routinely with the same ease and convenience of Most users of the amphibole nomenclature will electron microprobe analyses, empirical estimates want to classify amphibole compositions that have are probably the best alternative. been determined with the electron microprobe, The procedure of estimating ferric iron will re­ which cannot distinguish among the valence states quire at least one recalculation of the all-ferrous of elements. This is unfortunate because it is analysis to a different cation sum. Consequently, clear that most amphiboles contain at least some familiarity with calculation of mineral formulae is ferric iron - see compilations of Leake (1968) and highly recommended for a fuller understanding of Robinson et al. (1982), for example. Conse­ the ferric estimation procedure. Thorough dis­ quently, the typical user of the amphibole nomen­ cussions of the calculation of mineral formulae clature will need to estimate empirically ferric can be found in the appendices of Deer et al. contents of amphiboles. (1966, 1992). The topic of ferric estimates in am­ Empirical estimates of ferric iron are not just phiboles has been discussed by Stout (1972), Ro­ poor approximations that suffice in the absence of binson et al (1982, p. 3-12), Droop (1987), Jacob- analytical determinations of ferric-ferrous ratios. son (1989), J. Schumacher (1991) and Holland & Empirical estimates yield exactly the same results Blundy (1994). An example of the recalculation of as analytical determinations of ferric iron, if (1) an electron microprobe analysis and the procedure the analysis is complete (total Fe plus all other for estimating minimum and maximum ferric con­ elements), (2) the analytical determinations are tents are given at the end. accurate and (3) the mineral stoichiometry (ideal anion and cation sums) is known. In the case of amphiboles, condition (3) cannot be uniquely Empirical ferric iron estimates determined because the Λ-site occupancy varies. for amphiboles However, knowledge of amphibole stoichiometry and element distribution can be used to estimate a The basic formula range of permissible structural formulae and ferric contents. Present knowledge of amphibole crystal chem­ The most welcome circumstances will be istry suggests that many amphiboles contain es­ where the difference between the limiting structur­ sentially ideal stoichiometric proportions of 2 al formulae are trivial, and the entire range plots (OH) and 22 O. These anions can be rearranged to within the same classification field. However, give the anhydrous formula basis 23 O (+ H2O), there will also be cases where the range of stoi- and calculation of the anhydrous formulae on this chiometrically allowable formulae is broad and basis is the first basic assumption necessary to es­ span two or more fields in the classification. Some timate ferric Fe. The ideal cation sums in amphi­ users of the amphibole nomenclature may con­ bole formulae are not fixed and can vary between sider this as less than satisfactory solution, but, 15 and 16 cations per 23 O (anhydrous). Conse-

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Summary of site assignments and stoichiometric constraints

Site and Stoichiometric Correction Occupancy Cation* Limit Minimum I Maximum

T-site Si <8 8Si i Al_ ΣAI > 8 8S1AI Ti C-site Cr + Fe3 Fig. 1. Summary of ideal site assign­ Mg ments, limits of various cation subto­ Ni tals and the type of correction (mini­ mum or maximum) that can be ob­ Zn tained by calculating the formulae to B-site Fe2+ these stoichiometric limits (after J. 1 Mn_ Schumacher, 1991). ΣMn> 13 l3eCNK Abbreviations of normalizations: 8Si = Ca_ ΣCa< 15 l5eNK normalized such that total Si = 8; Na_ 8SiAl = normalized such that total Si ΣNa> 15 !5eK A-site K _ +A1 = 8; 13eCNK = normalized such ΣK < 16 I6CAT that total the sum of the cations Si I D through Mn (i.e., all cations exclusive of Ca,Na,K) =13; 15eNK = nor­ * cations arranged according to increasing ionic radius malized such that total the sum of the (smallest, Si to largest, K) cations Si through Ca (i.e., all cations Σ = cation subtotal (e.g. ΣMn = sum of all cations from Si through Mn exclusive of Na,K) = 15; 16CAT = in the list) normalized such that total the sum of D = vacancy at the A-site all cations = 16 (see also Robinson et aL, 1982, p. 6-121).

quently, it is not possible to arive at at unique fer­ phibole formulae will satisfy all six of these crite­ ric estimation based on stoichiometry, as can be ria. Exceeding one or more of these stoichiometric done for minerals with fixed ratios of cations to limits indicates that there are problems with the anions (e.g. pyroxenes or the ilmenite-hematite structural formula, and the identity of the unful­ series). Nevertheless, based on our present under­ filled condition will suggest the cause. standing of permissible and usual site occupan­ For minerals that bear ferric iron, the all-fer­ cies, limits can be placed on the maximum and rous structural formulae will have cation sums minimum values of ferric contents, and these that are too high (for discussion see J. Schu­ limits yield a range of acceptable mineral formulae. macher, 1991 and refs. therein). In amphiboles, this can result in violation of at least one of the criteria Si <8, ΣCa< 15 or ΣK< 16 (Fig. 1). Viola­ Critical examination of electron tions of the other three criteria, ΣAI > 8, ΣMn > 13 microprobe analyses and ΣNa> 15 (Fig. 1), cannot be due to failure to account for ferric iron and usually indicate an ana­ The suitability of an electron microprobe analyses lytical problem (too few cations at some of the of an amphibole for a ferric estimation requires sites1.) These analyses should not be used for em­ the evaluation of the all-ferrous, anhydrous for­ pirical ferric estimates. mula that is calculated on a 23 oxygen basis. The site assignments can be used to evaluate the anal­ yses, and these are given in Fig. 1). From the site exceptions do exist: potassium titanian richterite (Oberti assignement data, it is possible to define the im­ et aL, 1992) has Ti at the tetrahedral sites and cannilloite portant stoichiometric limits (cation subtotals) for which has 1 Ca at the A and 2 Ca at the B (M4) positions. the amphiboles (column 3, Fig. 1). Acceptable am­ These exceptions are rare.

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Minimum and maximum estimates Table 1. A hypothetical amphibole analysis. The struc­ tural formulae that are based on the chemical and stoi­ For many amphibole analyses, none of the criteria chiometric limits. The ferrous formula assumes total Fe Si < 8, ΣCa< 15 and ΣK< 16 will be exceeded by as FeO, the ferric formula assumes total Fe as Fe2O3. the all-ferrous formula, the minimum ferric esti­ The 13eCNK and 15eNK formulae are based on stoi­ mate is the all-ferrous formula (i.e. Fe3+ = 0.000 chiometric limits. See text for discussion. and the site occupancies of all-ferrous formula are all allowable). If one or more of the three criteria Analysis Formulae Si< 8, ΣCa< 15 and ΣK< 16 are exceeded, ferric (wt %) All All Fe may be present, and a minimum ferric estimate Ferrous 15eNK 13eCNK Ferric can be made that will yield a formula with accept­ Si02 39.38 Si 6.093 6.081 6.000 5.714 able stoichiometry. The condition that is most Al203 16.70 Al 1.907 1.919 2.000 2.286 FeO 23.54 Σ 8.000 8.000 8.000 8.000 greatly exceeded determines the basis for the re­ MgO 4.40 calculation. For example, if Si = 8.005, ΣCa = CaO 11.03 Al 1.139 1.122 1.000 0.571 15.030 and ΣK = 15.065, then the ΣSi limit is ex­ Na20 2.37 Fe3+ 0.000 0.088 0.700 2.857 Mg 1.015 1.014 1.000 0.952 ceeded by 0.005 and the ΣCa by 0.030. Since ΣCa Total 97.42 Fe2+ 2.845 2.777 2.300 0.000 is in greatest excess, the minimum ferric estimate Σ 5.000 5.000 5.000 4.380

is obtained by recalculating the formula so that Fe2+ 0.201 0.176 0.000 0.000 ΣCa = 15.000 (15eNK estimate, Fig. 1). Ca 1.799 1.824 1.800 1.714 The maximum ferric estimates are obtained Na 0.000 0.000 0.200 0.286 Σ 2.000 2.000 2.000 2.000 from the stoichiometric limits ΣA1>8, ΣMn > 13 and ΣNa>15 (Fig. 1). The condition that is nearest Ca 0.029 0.000 0.000 0.000 to the minimum value of one of these sums gives Na 0.711 0.709 0.500 0.381 the maximum ferric estimate. For example, if ΣA1 Sum 15.740 15.709 15.500 14.761 = 9.105, ΣMn = 13.099 and ΣNa = 15.088, then ΣA1 is exceeded by 1.105, ΣMn by 0.099 and ΣNa by 0.088. The ΣNa is nearest the minimum value, values for ΣA1, ΣMn and ΣNa are, respectively, and recalculating the formula so that ΣNa = 8.000, 13.000 and 15.000 and the actual values 15.000 (15eK estimate, Fig. 1) will give the maxi­ are 9.139, 13.201 and 15.740. mum ferric formula. These formulae for the minimum and maxi­ mum ferric estimates can be calculated in either of Recalculation of the formulae two ways: (1) by normalizing all the cations of the all-ferrous formula that were calculated on a 23 The recalculation procedure is described step-by- oxygen basis such that ΣCa = 15.000 and ΣMn = step at the end of this discussion, but some gen­ 13.000 (i.e., cations of each element multiplied by eral aspects are discussed here. Table 1 lists a hy­ 15÷ΣCa or 13 ÷ΣMn, here 15 ÷15.029 = 0.9981 pothetical amphibole analysis (wt%) and four and 13 ÷ 13.201 = 0.9848, respectively), or (2) by formulae that are based on 23 oxygens. Formulae using the normalization factor to determine the were calculated for the two chemical limits (all new cation sum and then recalculating the entire iron as FeO or Fe2O3>; the other two are the stoi­ formula on cation bases that set ΣCa = 15.000 and chiometric limits (see Fig. 1) which give the mini­ ΣMn = 13.000. The second method requires more mum (15eNK) and maximum (13eCNK) ferric es­ calculation, but J. Schumacher (1991) has shown timates. All of the stoichiometric limits except that this method leads to fewer rounding errors ΣCa< 15 (here ΣCa = 15.029) are met by the all- than normalizing the cations in the 23 oxygen- ferrous formula, which means that the minimum based formula. ferric formula is given by with the 15eNK esti­ The formula obtained from either recalcula­ mate (Table 1). tion method will have less than 23 oxygens. The Since ΣMn is nearest the lowest allowable cations of ferric iron (Fe3+) are found by calculat­ sum, the maximum ferric estimate values, and the ing the number of moles of FeO that must be con­ ferric formula is obtained by recalculating as be­ verted to FeO! 5 to bring the sum of the oxygens to fore, but, in this case, the normalization must in­ 23 and equals (23-ΣOx)×2, where ΣOx is the sure that ΣMn = 13.000 (here the normalization sum of the oxygen in the normalized formula (ΣOx factor is: 13+13.201 = 0.9848). The minimum = ΣR4×2+ΣR3×1.5 + ΣR2 + ΣR1×0.5, where ΣR

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Limits on ferric-Fe estimates inamphiboles

IX X v I range of possible formulae All ferrous Fe (chemical limit) ^Myy stoichiometric assumptions 15eNK (stoichiometric limit), All ferric Fe 13eCNK 16CAT (chemical limit) (stoichiometric limit) 15eK (stoichiometric limit) (stoichiometric limit) 16 I L - xcations 1 ' ications eNK - - 14 . ΣCations eCNK - • 12H c

= the sums of cations with the same valence). The electron microprobe analysis, and, on such a dia­ 3+ moles of FeO equal FeT-Fe where Fej = total gram, the range of both the chemical and the ap­ Fe in the normalized formula. Following any re­ propriate set of stoichiometric limits could vary calculation, it is good practice to recheck to see greatly from example to example. It can be in­ that all six stoichiometric limits are also satisfied ferred from Fig. 2 that the range of permissible by the new ferric formulae. amphibole formulae could be, and commonly is, bounded by one of the chemical limits and one of the stoichiometric limits. Discussion of the recalculation results The relationships among cations sums that are illustrated in Fig. 2 shows that comparison of The variation in some cation values within the some of the possible normalization factors, which ranges of possible formulae (Table 1) that are are obtained from the stoichiometric limits, can be defined by the chemical and stoichiometric limits used to (1) check the applicability of a specific are compared in Fig. 1. In general, the range of ferric estimate and (2) determine limits, chemical possible formulae that are defined by the stoi­ or stoichiometric, give the minimum and maxi­ chiometric limits will be much narrower than the mum ferric estimates. To accomplish this, all the range obtained from the two chemical limits. A di­ normalization factors for all stoichiometric con­ agram like Fig. l could be constructed for every straints and the chemical limits must be compared

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(see Fig. 1). The normalization factors for the stoi- ferrous formula. For the analysis in Table 1, this chiometric constraints are calculated from the all- normalization factor (here abbreviated: 10ΣFe3+) ferrous formula using the data in Table 1 and are: is 0.977, which is less than the 0.983 value of the 13eCNK factor, so the 10ΣFe3+ normalization will Minimum ferric estimate: not give the maximum ferric estimate in this case. 8Si = 8/Si = 8/6.093 = 1.313, (1) Most users of the nomenclature will want to 16CAT = 16/ΣK = 16/15.740 = 1.017, (2) report only a single mineral formula and name for all ferrous (no change) = 1.000, (3) each amphibole analysis; consequently, the over­ 15eNK = 15/ΣCa = 15/15.029 = 0.998, (4) riding question is: which correction should be Maximum ferric estimate: used? Unfortunately, there is no simple rule, and 13eCNK = 13/ΣMn = 13/13.201 = 0.985, (5) each group of similar analyses may require indi­ 15eK = 15/ΣNa = 15/15.740 = 0.953, (6) vidual treatment - Robinson et al. (1982, p. 11) all ferric = 0.938, (7) and J. Schumacher (1991, p. 9-10) discuss some 8SiAl = 8/ΣA1 = 8/9.139 = 0.875. (8) of these possibilities for Fe-Mg, calcic, sodic-cal- cic and sodic amphiboles in greater detail. The 3+ For the normalizations that yield minimum es­ 10ΣFe correction discussed in the preceding timates (1 to 4), the recalculation that requires the paragraph will not likely be important in Ca am­ lowest normalization factor will be the minimum phiboles, but in sodic amphibole (e.g., riebeckites, ferric estimate. For the normalizations that yield glaucophanes) may commonly yield the maxi­ maximum estimates (5 to 8), the recalculation that mum ferric estimate. requires the largest normalization factor will be Choosing a single representative ferric for­ the maximum ferric estimate. All normalizations mula out of the range of possible formulae re­ that lie in between these values (in this example, quires further justification or making additional 0.998 and 0.985) will give stoichiometrically ac­ assumptions. One solution is to use the mean ceptable formulae. If any of the normalization fac­ value between maximum and minimum ferric tors for the maximum estimate (5 to 8) are greater contents (Spear & Kimball, 1984). Other solutions than any of those for the minimum estimate (1 to can be obtained for restricted types of amphibole. 4), then the analysis is not suitable for empirical For example, R. Schumacher (1991) derived a ferric Fe estimations. Note that normalization fac­ normalization scheme that yields formulae inter­ tors greater than 1.000 or less than the normaliza­ mediate to maximum and minimum ferric formu­ tion factor for the all-ferric formula would yield lae for calcium-saturated, metamorphic horn­ impossible ferric estimates that lie outside of the blendes and is based on regression analysis of chemical limits. hornblende compositions for which ferric-ferrous In addition to the stoichiometric constraints determinations were known. listed in Fig. 1, another constraint on maximum Generally, it will be desirable to determine the ferric Fe can be defined if the C site in the formu­ extent to which the minimum and maximum ferric lation of the amphibole nomenclature is further estimations affect the classification of the amphi­ subdivided. The five C positions consist of 3 mica­ bole in question by inspecting the formulae of like, two Ml octahedra and one M3 octahedron, both the maximum and minimum ferric estimates. and two pyroxene-like M2 octahedra. The cations If the entire range formulae give a wide spectrum Al,Fe3+, Ti and Cr3+ are strongly partitioned into of possible names, this should probably at least be the M2 octahedra. Consequently, an additional mentioned where ever the amphibole is being de­ maximum ferric estimate can be obtained by as­ scribed. suming all the tetrahedral and M2-octahedral sites are completely filled with cations of valences of Deviations from the basic assumptions 3+ and 4+. This normalization factor (N) can be calculated by solving the two simultaneous equa­ F and Cl substitutions tions for N: (1) N×(Si+Ti + Al + Cr)+Fe3+ = 10, Both F and Cl may substitute for (OH) in the am­ which describes desired resulting stoichiometry phibole structure, and these elements are not rou­ and (2) Fe3+ = (23-23 ×N)×2, which gives the tinely determined at all electron microprobe fa­ ferric Fe for this normalization. The solution for N cilities. Although it is highly recommended that is: N = 36/(46-Si-Ti-Al-Cr) where Si, Ti, Al these elements also be determined, their presence and Cr are the amounts of these cations in the all has no effect on the ferric estimation procedure.

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Exchange of F or Cl for OH does not change the various crystal-chemical constraints allow a range total number of negative charges (-46) in the an­ of possible formulae that give the minimum and hydrous amphibole formula, so the proportions of maximum ferric contents to be determined. cations required to give 46 positive charges will Selecting a single structural formula from the be independent of the proportions of OH, F or Cl range of possibilities requires applying an addi­ that are present. The critical assumption is that tional constraint or making a further assumption, exactly two anions [OH, F, Cl] are present for such as using the formula that gives minimum, every 22 oxygens. maximum or the mean ferric iron, or applying some petrologic constraint. In written descriptions, Coupled substitutions involving anions it will be important to report the analyses, which The validity of a basic 23 oxygen anhydrous am­ enables others to do their own recalculations, and phibole formula (i.e. exactly two OH+F+C1) is an a clear statement of the method and assumptions underlying assumption in the procedure to esti­ that were used to calculate the given structural mate ferric iron in amphiboles. Any variation in formula. these values will have a tremendous effect on the The users of the IMA amphibole nomenclature ferric iron estimation. The partial replacement of ought to explore the formulae for the minimum [OH+F+Cl] by O in the amphibole structure is an and maximum ferric estimates. This defines the example of this kind of variation and has long range of possible formulae and possible names. been recognized. Amphiboles that are referred to Since, some amphibole names carry special petro- in numerous mineralogy and optical mineralogy genetic significance, care should be taken if the textbooks as "basaltic hornblende" (Deer et ah, range of possible names is large. 1966), or the kaersutite end member of the IMA amphibole nomenclature, can show this type of compositional variation. Worked example: Intuitively, one would expect analytical totals Calculation of a mineral formula and to be affected by variable O/OH; however, since a ferric estimate from these amphiboles tend to be richer in ferric Fe, the an electron microprobe analysis increase in the sum from the partial exchange of O of an amphibole for OH tends to be offset by treating the larger amounts of Fe2O3 as FeO. Consequently, even in As an example (Table 2), the analysis that appears anhydrous amphiboles with significant ferric Fe, in Deer et al. (1992, p. 678) was chosen. To simu­ no compelling evidence of these substitutions will late analysis by electron microprobe the ferric iron necessarily be seen in the analyses. Ferric estima­ was recast as ferrous iron and the water analysis tion can still be carried out on analyses with vari­ was ignored. The ferric estimate was made assum­ able O/OH, but an additional estimate of the H2O ing 2 (OH) are present rather than the 2.146 sug­ and halogen content will be an essential additional gested by the actual water determination. Any dis­ requirement. crepancies in the final decimal places of the numbers that appear below and in Table 2 are due to rounding effects. Conclusion (1) Divide each wt% (column 1) by the molecular Amphiboles typically contain at least some and wt of the oxide to yield the molecular proportion may contain significant amounts of ferric iron; of each oxide (column 2). [e.g. for SiO2 51.63 ÷ however, the most common analytical method, the 60.085 = 0.85928]. electron microprobe, cannot distinguish among valence states. The ferric contents of amphiboles (2) Obtain atomic proportions of the cations (col­ can be estimated providing that all chemical anal­ umn 3) and atomic proportions of the oxygens ysis are complete and ideal stoichiometry (site oc­ (column 4) by multiplying each molecular pro­ cupancy) can be assumed. If these conditions portion value by the number of cations and hold, empirical estimates of ferric iron would oxygens in the oxide, [e.g. for SiO2: 0.85928x1 = have the comparable accuracy and precision as 0.85928 and 0.85928x2 = 1.71857]. ferric-ferrous determination. For amphiboles, stoi­ Note: Assuming 2 (OH) groups are present, 1 chiometry cannot be uniquely determined, but oxygen is balanced by 2 H (i.e. H2O) so the cation

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Table 2. A worked example of an amphibole analysis that appears in Deer et ai (1992, p. 678). See the end of the text for a step-by-step discussion of this table.

1 2 3 4 5 6 Atomic Atomic anions on cations on Molecular Proportions Proportions the basis of the basis of wt% Proportions (cations) (oxygens) 23 oxygens 23 oxygens col. 2 × col. 2 × wt% + cations in oxygens in col. 4 × col. 3 × mol. wt. oxide oxide 8.45012 8.45012 Si02 51.63 0.85928 0.85928 1.71857 14.52208 7.261

Ti02 0.00 0.00000 0.00000 0.00000 0.00000 0.000 AI2O3 7.39 0.07248 0.14496 0.21744 1.83736 1.225

Cr203 0.00 0.00000 0.00000 0.00000 0.00000 0.000 RO 7.55 0.10509 0.10509 0.10509 0.88799 0.888 MnO 0.17 0.00240 0.00240 0.00240 0.02025 0.020 MgO 18.09 0.44884 0.44884 0.44884 3.79274 3.793 GO 12.32 0.21969 0.21969 0.21969 1.85641 1.856 NéfcO 0.61 0.00984 0.01968 0.00984 0.08317 0.166 K20 0.00 0.00000 0.00000 0.00000 0.00000 0.000

sum 1.79994 2.72185 23.0000 15.210

Factor for the recalculation of atomic proportions to 23 O basis: 23 + 2.72185 = 8.45012

7 8 9 1 0 1 1 1 2 1 3 Min. formula col. 8× Formula Formula Formula ideal site from cations col. 6× oxygen ideal site (15βNK) (15eK) Average of Min Formula assignments col. 6 0.99714 per cation assignments minimum Fe3+ maximum Fe3+ and Max. Fe3+ from DHZ Si 7.261 Si 7.240 7.161 7.201 7.196 ! IV AI 0.739 Al'v 0.760 0.839 0.799 0.804 sum T 8.000 Si 7.2401 14.4802 sum T 8.000 8.000 8.000 8.000 VI AI 0.486 AI 1.2214 1.8321 AIVI 0.462 0.369 0.416 0.410 3+ Fe 0.000 Ti 0.0000 0.0000 Fe3+ 0.133 0.634 0.383 0.263 Cr 0.000 Cr 0.0000 0.0000 Cr 0.000 0.000 0.000 0.000 Mg 3.793 Mg 3.7818 3.7818 Mg 3.782 3.740 3.761 3.759 2+ Fe 0.721 Fe2+ 0.8854 0.8854 Fe2+ 0.624 0.242 0.440 0.618 Mn 0.000 Mn 0.0202 0.0202 Mn 0.000 0.015 0.000 0.000 sum C 5.000 Ca 1.8511 1.8511 sum C 5.000 5.000 5.000 5.000 Mg 0.000 Na 0.1659 0.0829 Mg 0.000 0.000 0.000 0.000 2+ Fe 0.167 K 0.0000 0.0000 Fe2+ 0.129 0.000 0.057 0.050 Mn 0.020 sum 15.1659 22.9337 Mn 0.020 0.005 0.020 0.020 Ca 1.856 Ca 1 .851 1.831 1.841 1.840 z ΣCa (col. 7) 0.090 Na 0.000 Na 0.000 0.164 0.082 sum B 2.043 2.000 15 + 15.043 = 0.99714 sum B 2.000 2.000 2.000 Na 0.166 Na 0.166 0.000 0.083 0.074 K 0.000 (23-22.9337) ×2 K 0.000 0.000 0.000 0.000 sum>4 0.166 = 0.1325 sum A 0.166 0.000 0.073 0.074 total 15.210 total 15.166 15.000 15.083 15.074 0.885-0.133 = 0.753

charges are balanced by the remaining 23 oxygens (23 ÷ the sum of column 4) [e.g. 23÷2.72185 = which is the basis of the anhydrous amphibole 8.45012; for SiO2: 1.71857x8.454012 = 14.52208]. formula (see text for discussion: it can be shown (4) Obtain the cations on the basis of 23 oxygens that, even if F and Cl have not been determined, (column 6) by multiplying each value in column 3 as long as OH + F + Cl = 2 the 23 oxygen formula by 23÷ the sum of column 4 [e.g., for SiO : will give the correct mineral formula). 2 0.85928x8.45012 = 7.261]. (3) Obtain the anions based on 23 oxygens (col­ Note: Column 6 is the all ferrous mineral for­ umn 5) by multiplying each value in column 4 by mula for the amphibole. Assigning the cations to

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sites shows if any deviations from ideal stoichio- normali­ metry can be explained by failure to account for calculation zation ferric iron. limit method calculation factor

(5) Ideal site assignments (column 7) are made Calculations for minimum ferric estimates from the cation values in column 6 - a general 8Si 8÷Si 8+7.261 1.1018 procedure is: 16CAT 16÷ΣK 16+15.210 1.0519 all ferrous - - 1.0000 (a) the 8 tetrahedral (T) sites 15eNK 15÷ΣCa 15+15.043 0.997 Γ - place all Si here, if Si < 8, then place all Si+Al here Calculations for maximum ferric estimates (b) the 5 octahedral (C) sites (M2, Ml, M3) 15eK ΣNa 15+15.210 0.9862+ - place Al remaining from step (a), Ti, 13eCNK ΣMn 13+13.187 0.9858 Fe3+ (initially = 0), and Cr here. In the all ferric [23 + (0.5×Fe2+)] 23+23.444 0.9811 following order, place enough Mg, Fe + 10ΣFe3+ (46-Si-Al-Ti-Cr) 36+37.5141 0.9596 and Mn to bring the total to 5. 8SiAl ΣA1 8+8.486 0.9427 - If Σ(A1VI... Mn) < 5, then place all these *Indicates normalizations that yield either the minimum or maxi­ elements here. mum ferric estimates (c) the 2 (B) sites (M4) - place any Mg, Fe + or Mn and Ca re­ maining after step (b) here ferrous formula (Fe3+ = 0.000) is the lower limit. - if Σ(Mg...Ca) at B <2, fill the remain­ In this example, the 15eNK normalization factor ing sites with Na to bring the total to 2 is the lowest. (d) the single large (A) site To obtain the formula that gives the minimum - place any remaining Na and K here. ferric estimate (column 8), multiply the cations from column 6 by the 15eNK normalization factor (6) Evaluating the structural formula. 0.99714(15+15.043). If any site has less than their ideal values (t = (8) Find the sum of oxygen (22.9337) in the nor­ 8.000, C = 5.000, B = 2.000, A = 0.000 to 1.000), malized formula by multiplying each single cation then a ferric estimate is either impossible or only value (column 8) by the number of balancing possible with additional constraining information. oxygens [e.g. for SiO : 7.240x2 = 14.4802; for This could also indicate an analytical problem 2 A1OJ5: 1.2214x1.5 = 1.8321; for MgO: 3.7818x1 The suitability of the analysis for a ferric esti­ = 3.7818; for NaO . : 0.1659x0.5 = 0.0829]. mation and the normalizations that yield the maxi­ 0 5 mum and minimum estimates of ferric iron can be (9) Ferric Fe equals the amount of ferrous Fe that determined by calculating the normalization fac­ must be converted to bring the total oxygens up to tors for all the various stoichiometric and chemi­ 23. The amount is (23-22.9337) × 2 = 0.133. cal limits. These are given below and are obtained (10) The new ferrous Fe value is the total Fe from from columns 6 or 7 (see Table, right). column 8 minus the ferric Fe [e.g. 0.885-0.133 = If the all the normalization factors (8Si, 0.753]. 16CAT and 15eNK) are greater than all the nor­ malization factors (8SiAl, 15eK, 10ΣFe3+ and (11) Recast the normalized cations as in step 5 13eCNK), then a minimum and a maximum ferric (column 10). This should yield a formula with no estimation can be calculated; if not, then no esti­ violations of the ideal stoichiometry. mation is possible. Note: Step 11 double checks the correctness of your calculations. It also is a check of whether (7) Minimum ferric estimates. correcting the initial stoichiometric violation will The lowest normalization factor among the four produce another [here, insufficient cations to fill T choices, 8Si, 16CAT, 15eNK and all ferrous, or C could result from the 15eNK normalization. determines the the formula that yields the mini­ Such analyses cannot be used for ferric Fe esti­ mum ferric estimate. If the factors 8Si, 16CAT mates (unfortunately, a lot of calculating is in­ and 15eNK are all greater than 1.000, then the all- volved in determining this)].

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(12) Maximum ferric estimates. Dyar, M.D., Mackwell, S.J., McGuire, A.V., Cross, L.R., Robertson, J.D. (1993): Crystal chemistry of Fe3+ The largest normalization factor among the four and H+ in mantle kaersutite: Implications for mantle choices, 8SiAl, l5eK, 13eCNK and all-ferric, metasomatism. Am. Mineral 78, 968-979. determines the the formula that yields the maxi­ Holland, T. & Blundy, J. (1994): Non-ideal interactions mum ferric estimate. If the factors 8SiAl, 15eK in calcic amphiboles and their bearing on amphi- and 13eCNK are all less than the all-ferric value, bole-plagioclase thermometry. Contrib. Mineral Petrol, 116, 433-447. then the all-ferric formula would give the maxi­ 3+ mum Fe3+. In this example, the 15eK normaliza­ Jacobson, C.E. (1989): Estimation of Fe microprobe analyses: obsrevations on calcic amphibole and tion factor is the largest and can be used to give 3+ chlorite. J. metamorphic Geol, 7, 507-613. the formula with maximum Fe . Leake, B.E. (1968): A catalog of analyzed calciferous To obtain the formula that gives the maximum and sub-calciferous amphiboles together with their ferric estimate (column l l), repeat steps 8 through nomenclature and associated minerals. Geol Soc. 10 for using the 15eK normalization factor Amer., Spec. Pap., 98, 210 pp. 0.98621 (15 ÷ 15.210). Oberti, R., Ungaretti, L., Cannillo, E., Hawthorne, F.C. (1992): The behaviour ofTi in amphiboles: . Four- (13) Average of the maximum and minimum fer­ and six-coordinate Ti in richterite. Eur. J. Mineral, ric estimates. 4, 425-439. Robie, R.A., Hemingway, B.S., Fisher, J.R. (1978): To obtain the formula that gives the average of the Thermodynamic properties of minerals and related maximum and minimum ferric estimates (col­ substances at 298.15 K and 1 bar (105 Pascals) umns 10 and 11), repeat steps 7 through 10 for pressure and at higher temperatures. U.S. Geol. using the average of the normalization factors that Surv. Bull, 1452,456 pp. were obtained in steps 7 and 12. This normaliza­ Robinson, P., Spear, F.S., Schumacher, J.C., Laird, J., tion factor is 0.99167 [(0.99714 +0.98621) ÷ 2]. Klein, C, Evans, B.W., Doolan, B.L. (1982b): Phase relations of metamorphic amphiboles: natural (14) The actual formula (column 12) given in occurrence and theory. In Veblen, D.R. & Ribbe, Deer et al. (1992) lies approximately between the PH. (eds.), Reviews in Mineralogy, Vol. 9B, Am­ minimum (15eNK) in column 10 and maximum phiboles and other hydrous pyriboles-mineralogy, (15eK) in column 11, but is nearer to the mini­ 227 pp. Schumacher, J.C. (1991): Emprical ferric iron correc­ mum. tions: necessity, assumptions, and effects on se­ lected geothermobarometers. Min. Mag., 55, 3-18. References Schumacher, R. (1991): Compositions and phase rela­ tions of calcic amphiboles in epidote- und clinopy- Deer, W.A., Howie, R.A., Zussman, J. (1966): An Intro­ roxene-bearing rocks of the amphibolite and lower duction to the Rock-forming Minerals. Longman granulite facies, central Massachusetts, USA. Con­ Group Limited, London, 528 pp. trib. Mineral. Petrol, 107, 196-211. (1992): An Introduction to the Rock-forming Spear, F.S. & Kimball, C. (1984): RECAMB - A FOR­ Minerals - 2nd ed. Longman Group UK Limited, TRAN IV programm for estimating Fe3+ contents Essex, 696 pp. in amphiboles. Computers and Geoscience, 10, Droop, G.T.R. (1987): A general equation for estimating 317-325. Fe3+ in ferromagnesian silicates and oxides from Stout, J.H. (1972): Phase petrology and mineral chem­ microprobe analyses^ using stoichiometric criteria. istry of coexisting amphboles from Telemark, Nor­ Mm. Mag., 51, 431-435. way. J. Petrol, 13, 99-145.

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