sign in sign up
<<
Home , Aegirine, Augite, Coupled substitution, Hedenbergite, Omphacite, Pyroxene

American Mineralogist, Volume 73, pages I I 2 3- I I j 3' I 988

Nomenclatureof Subcommittee on Pyroxenes Commission on New and Names International Mineralogical Association N. Momvroroo Chairman Department of Geology and , Kyoto University, Kyoto 606' Japan SubcommitteeMembers J. F.LsRrns(France), A. K. FnncusoN (Australia)I. V. GrNzruRG(USSR), M. Ross (U.S.A.), F. A. Srmnnr (Germany),J. ZussMAN (U.K.) NonvotingMembers K. Aoxr (Japan),G. Gorr.l'nor (Italy) Ansrucr This is the final report on the nomenclature of pyroxenes by the Subcommittee on Pyroxenesestablished by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The recommendations of the Subcommittee as put forward in this report have been formally acceptedby the Commission. Accepted and widely used names have been chemically defined, by combining new and conventional methods, to agreeas far as possiblewith the consensusof presentuse. Twenty names are formally accepted,among which thirteen are usedto representthe end membersof definite chemical compositions. In common binary -solution series,species names are given to the two end members by the "500/oruIe." Adjectival modifiers for mineral names are defined to indicate unusual amounts of chemical constituents.This report in- cludesa list of 105 previously used pyroxene names that have been formally discardedby the Commission.

INrnooucrroN present use. Two kinds of adjectival modifiers are used: one to specify a part of the compositional range shown The Subcommittee on Pyroxeneshas, after a thorough by a mineral that forms a wide solid solution [e.g.,mag- evaluation ofthe group ofpyroxene minerals, presented nesium-rich (or Mg-rich) augiteand -rich (or Fe-rich) its recommendationsfor a new classificationand nomen- augitel; the other to specifo elemental substitutions that clature to the Comrnission on New Minerals and Mineral are not essentialconstituents (e.g., titanian ). The Names (hereafter abbreviated as CNMMN). These rec- CNMMN has formally discredited 105 previously used ommendations have been approved by the Commission pyroxene names-mostly synonyms, obsolete or almost by a formal vote (May 20,1987). unused, or recommendedfor rejection. The classification and nomenclature of the pyroxenes General publications dealing with the pyroxene group have been largely based on their chemistry. In include -Forming Minerals (Deer et al., 1978),Min- practice the chemical content of the pyroxene formula eralogical Society of America Special Paper 2 (Papike, unit calculated to six ,or to four cations (Vieten 1969) and MSA Revkws in Mineralogy, volurne 7 (Prew- and Hamm, 1978),is essentialfor the classification.This itt, 1980), which provide referencesto the voluminous formula unit correspondsto one-quarter of the unit cell literature. for the monoclinic pyroxenes and to one-eighth of the unit cell for the orthorhombic pyroxenes.The basic prin- Cnvsr.lr, CHEMISTRYoF THE PYRoxENES ciple adopted for nomenclature (kake and Pyroxenes are that, in their simplest form, Winchell, 1978) is to denote principal stoichiometriesby contain singleSiO, chains oflinked SiOotetrahedra. Gen- generally well-establishednames, with adjectival modi- erally, small amounts of Si are replacedby Al and other fiers to indicate the presenceof substantial substitutions small cations. The repeat along the chain (c axis) com- that are not essential constituents of the end members; prises two tetrahedra and is approximately 0.52 nm in this principle has been followed as far as possible in the length. The general chemical formula (formula unit) for pyroxene nomenclature. all pyroxenes'is M2MlTrOu, where M2 refers to cations No new names have been introduced in the proposed nomenclature. Accepted and widely used names have been chemically defined by combining new and conventional I In -P2/n,the Ml and M2 sitesare further divided methods to agreeas far as possiblewith the consensusof into Mla and Mlb (for Ml) and M2a and M2b (for M2). 0003{04v88/09 I 0-l I 23$02.00 tt23 n24 MORIMOTO:NOMENCLATURE OF PYROXENES

gens and four cations by adjusting the ratios Fe2*/Fe3*, Ti4+/Ti3+,etc. The standard pyroxene formula M2MlTrO6 contains two tetrahedral sites. In the allocation of the cations to obtain a pyroxene formula, the following procedure is recommended:

-3+ 1. Sum T to 2.000 using Sia*,then Al3*, and then Fe3t. !e 2. Sum Ml to 1.000using all Al3* and Fe3*in excess Ti4+ of that used to fill the T sites. If there is insufficient Al3* 1+ Cr- and Fe3*to sum to 1.000,then add Tia*, Cr3*,V3+, Ti3+, ..3+ Zra*, Sc3', Zn2*, Mg2', Fe2*, and finally Mn,* until the ?+ sum is 1.000. Ti-' M2 A+ 3. Sum using all Mg2*, Fe2*,and Mn2t in excessof zt that used to fill the Ml sites. Then add Li*. Ca2*. and Na* so that the sum becomes 1.000 or close to it. If the

zn2+ sum is far from 1.000, one must be suspiciousabout the results of the analysis. tg2* - tf2* 2+' A flow chart (Fig. l) gives a diagrammatic representa- Fe2* - Fe- tion ofthe site allocation ofthe principal cations in py- l,t 12* - Itr2+ roxenes. However, because the distribution of cations I,i- among the Ml, M2, and T sites in a given pyroxene is partly a function of temperature, the accurate site occu- + pancy must be determined by structure determination. Na' The site occupancygiven in Figure I is called ideal site Fig. l. Flowchart for idealsite occupancy of cationsbetween occupancyto distinguish it from real occupancy.A meth- the T, Ml, and M2 sitesof pyroxenes.Only representativecat- od for classifuingpyroxenes by their ideal site occupan- areincluded. Arrows indicate order offilling ofsites.Real cies has been proposedby Bokij and Ginzburg (1985). In site occupancyis usually slightly different from the ideal site the present classifrcationof pyroxenes, the Ml and M2 occupancy. sites are considered together as a single M site in order to avoid the difference between the real and ideal site occupancles. in a generally distorted octahedral coordination. Ml to Starting from the most common pyroxene formula, cations in a regular octahedral coordination, and T to M2(R'z-)MI (R2*)Tr(2R4*)O6,four coupled substitutions tetrahedrally coordinated cations. are possible if one assumesmore than one Ra* in the T Any pyroxene belongs to either the orthorhombic or site. They are listed in Table l, where the elements in the monoclinic .There are two orthorhom- parenthesesare coupled substitutions. bic pyroxene types: (Pbca) orthopyroxene and orthopy- Substitution I encompassesthe end members roxene (Pbcn).,Only the former has been found in nature. (NaAlSirOu), (NaFe3*SirOu),kosmochlora Monoclinic pyroxenes are called clinopyroxenes. Their (NaCr3*SirO.,Ko), and jervisite (NaScSirOu,Je). Substi- space groups are C2/c, P2,/c, and P2/n, depending on tution 2 results in components such as NaFefrjTiftsi2o6, their chemical composition petrogenetic and history. but is less important than the other substitutions. Throughout this report, the standardpyroxene formula In substitution 3, the Al-Al couple is often referred to is usedwith superscriptedarabic numerals (e.g., Fe2*)re- as "Tschermak's component"; CaAlAlSiOu,in particular, ferring to chargesand subscripted numerals (e.g., MgJ is called " Tschermak's component." Substitu- referring to numbers of atoms. tion in esseneite,sCaFe3*AlSiO., is obtained by this type In order to derive a pyroxene formula from a chemical of substitution. This substitution is also important in analysis, the calculation should be based on six atoms when Fe2* and Fe3* are both determined. In mi- croprobe analyses,only total Fe is determined, and the 3"" is usedin preferenceto "acmite" in this report. option of calculating to four cations should at least be "Aegirine"is in commonusage in theliterature and is consistent permitted if not actually preferred. Vieten and Hamm with the almostuniversal use of "aegirine-augite"for minerals (1978) have shown that calculation to four cations will of intermediatecompositions, though "acmite" haspriority by years(Dana, practice be more reliable for microprobe analysesof the majority 14 1892).Common in experimentalpe- pyroxenes. trologyhas been to usethe abbreviationAc for NaFe3*SirO6;Ae of Therefore, for microprobe analyses,it is shouldnow be usedinstead. recommendedthat the componentsbe totaled to six oxy- 4The CNMMN, IMA, hasrecently voted in favorof thename ""instead of "ureyite" for the pyroxeneofgeneral- izedcomposition NaCrSirO.. 2 Orthopyroxene(Pbcn) is stahleonly at elevatedtemperatures 5Esseneite is a new pyroxenewith the compositionCa- for a limited composition near MgSiOr. Fe3*AlSiOuGable 2, no. l3). MORIMOTO:NOMENCLATURE OF PYROXENES tI25

TeeLe1. Fourcoupled substitutions. of pyroxenesin the stan- namesare given for the end-member componentsof sub- dardchemical formula R2+R2+R4+06 stitutions 2 and 4. Substitutionsite M1 Examples MrNBul NAMES oF THE PYRoXENES

Standardoccupancy R2* R2* 2R4* Twenty (20) mineral namesand their grouping Substitution1 (R) (R*) 2R4* Na-Al The pyroxenes form extensive solid solutions by var- Na-Fe3+ Na-C13* ious types of ionic substitutions, some of which are de- Na-Sc3* scribed above. To cope with the problem of pyroxene Substitution2 (R.) R63(R33) 2R4* Na-Oi4*/2) nomenclature, it is necessaryto subdivide the solid-so- Substitution3 R2* (R"t, (Rr+)Re AI-AI Fe+-Al lution seriesinto rangeswith specifiedcompositions and Cr3+-Al names. Whenever there is a complete solid-solution se- R6i(R6i) Substitution4 R2* (Rs+)R4+ (Ti4V2)-Al ries betweentwo end members,it is customary in mineral 'Shown by parentheses. nomenclature to use only two names, and the division betweenthem should be at AroBro(the "500/0rule"). How- ever, this "500/orule" cannot be applied rigorously to the "fassaite."6 Substitution resulting in CaTi3*AlSiOu was large groups ofpyroxenes that show wide rangesofcou- (1973) (1974) reported by Dowty and Clark and Mason pled substitutions. This is particularly so when the min- pyroxenes (Table in from the 3, no. 4). erals concerned are abundant and widespread and have In substitution 4, the component CaMgorTiS.SAlSiOuis a historically establishednomenclature in mineralogical pyroxenes. found in some There are a few instances of and petrologicalcircles. Taking this situation into consid- the component of substitution 2 or 4 amounting to nearly eration, 20 acceptedand widely used names have been (Table particular 500/0,as describedlater 3). However, no adoptedas mineral speciesnames of the pyroxenes(Table 2). 6"Fassaite" has the general formula Ca(Mg,Fe3*,Al)(Si,Al)rOu. The definition ofthe pyroxene specieshas been based This namehas been rejected as a formalname in this report. on 13 end members, or chemical components (given in

TnaLe2. Acceptedpyroxene mineral names and their chemical subdivisons

Mineral names Compositionas end member Main composition as solid solution Spacegroup A. Mg-Fepyroxenes 1. (En) MgrSirO6 (Mg,Fe),Si,O6 Pbca 2. ferlosilite (Fs) Fee+Sir06 3. clinoenstatite (Mg,Fe),StO€ nllc 4. clinoferrosilite 5. (Mg,Fe,CaLSLO6 PJc B. Mn-Mg pyroxenes 6. donpeacorite (Mn,Mg)MgSi,Os Pbca 7. kanoite (Ka) MnMgSi,O6 (Mn,Mg)MgStO6 PJc C. Ca pyroxenes 8. (Di) GaMgSi,O. Ca(Mg,Fe)St06 C2lc 9. (Hd) CaFe'*Sir06 10. augite (Ca,Mg,Fe),SirO6 C2lc 11. iohannsenite(Jo) CaMnSiro6 C2lc 12. petedunnite(Pe)' CaZnSi,O6 C2lc 13. esseneite (Es)". CaFe#AlSi06 C2lc D. Ca-Na pyroxenes 14. omohacite (Ca,NaXR'z*,Al)StOo C2lc, Pln 15. aegirine-augite (Ca,NaXR,*,Fes*)Si,O6 C2lc E. Na pyroxenes 16. (Jd) NaAlSiro6 iadeite Na(Al,Fe3+)SirOs C2lc 17. aegirine(Ae) NaFe3+Si2O6 18. kosmochlor(Ko) NaCre*Si2O6 C2lc 19. iervisite (Je)t NaScP*Siro6 C2lc F. Li pyroxene 20. (Sp) LiAtsi,o6

A/ote:Name, abbreviation, and compositionare given for any pyroxenethat is used as an end memberot a pyroxenesolid solution; such end members are printed in boldfacetype. Main compositionsare given for solid solutions. Space groups are also given. - Petedunnitehas been determinedby Esseneand Peacor(1987) to have the composition(CaopNao6Mno@Xzno3zMno ieFq:frF4lrMgo,.XSi, sAlo6)00 by means of an electron microprobe.This mineral was approved as a valid species by the CNMMN, lMA, in 1983. '-Esseneite has been determinedby Cosca and Peacor(1987) to have the composition(Ca,oNaoorxF6tMgo,6AloqTio6F4.[r)(Si,,rAlor,)O., by means of an electron microprobe.This mineralwas approved as a valid species by the CNMMN, lMA, in 1985. f Jervisite has been determined by M. Mellini et al. (1982) to have the composition (Nao€Caoo1F414troit(Sco6FqlsMgo,e)Sirooby means of an electron microprobe.This mineralwas approved as a valid species by the CNMMN, lMA, in 1982. tt26 MORIMOTO:NOMENCLATURE OF PYROXENES bold face in Table 2) and the component CarSirOu(Wo).' ries (adeite-aegirineseries). Subdivision namesof the in- Theseend members are given the names of the minerals termediate solid-solution ranges, such as , whose compositions they most closely approximate. The ,and eulite of the enstatite-ferrosilite series 20 pyroxene speciesare grouped into six chemical sub- and salite and ferrosalite ofthe diopside-hedenbergitese- divisions on the basis of the cation occupancyof the M2 ries, have been discarded. However, the 500/orule was sitesand crystal-chemicalsimilarity. This classificationis not applied rigorously to the Ca-Mg-Fe pyroxenes and a slight modification of the widely used schemeproposed Na-Ca pyroxenes.The widely acceptedterms such as au- by Deerer al. (1978). gite, pigeonite,omphacite, and aegirine-augiteehave been For the precise classificationof the pyroxenes into 20 retained. mineral however, species, the following characteristicsof Gem namesof spodumene the pyroxenes must be considered. First of all, the Mg- "hiddenite" are often used Fe pyroxenesand some of the Ca pyroxenesare the most Two names, and "kunzite," (pale) lilac

,ES

I I

I

Je Fig.3. The 103 Deeret tllzsl selected J ,r.o*.rrlrouo- "r. by Cameronand Papike (1981) plotted on the Q-./diagram.For Fig. 2. Q-J diagram for the pyroxenes,on which the posi thesepyroxenes, the O valuesare less than 1.90,and Mn is less tions of the I 3 acceptedend members have been indicated. Ab- than 0.08atoms per formulaunit. breviations and cornpositions of the end members are listed in Table 2. + Mg + Fe (Quad), Ca-Na, and Na pyroxenes. The boundariesdefined bv J/(Q + J):0.2 and 0.8 are used by Deer et al. (1978)and Cameronand Papike(1981). following equations are used to subdivide the Q-J dia- Becausethe Mn-Mg pyroxenes and johannsenite (Ta- gram: ble 2) have Mn ions occupying more than half of the M2 Q + J:2.0 (l) and Ml sites, respectively, they have Q values between Q+J:r.5 (2) 1.0 and 1.5 in the Q-J diagram. Similarly, petedunnite J/(Q + J): 0.2 (3) and esseneiteplot along the Q axis with Q valuesbetween : J/(Q +.I) 0.8. (4) 1.0 and 1.5. Spodumene plots at the origin of the Q-J The areascorresponding to the Ca-Mg-Fe pyroxenes,Ca- diagram becauseboth Qand J arezero. Thus, the thirteen Na pyroxenes, Na pyroxenes, and other pyroxenes are end members (Table 2) and Wo are located in the Q-J labeled (Fig. 2) Quad, Ca-Na, Na, and Others, respec- diagram (Fig. 2). tively. Application ofthis classificationprocedure to 406 py- In this diagram, ,Iis meant to include the total number roxeneanalyses presented in Deer et al. (1978) has shown of Na and R3*, usually Al, Fe3*,Cr3*, and Sc3*,that cou- that most of the analyses,except those of johannsenite ple with Na in substitution I mentioned in Table l. When and spodumene, are included in the area between the the in the pyroxene is not oftype I lines O + J : 2.0 and Q * J : 1.5. The 103 Deer et al. but of type 2 or 3, lhe J value apparently does not rep- (1978)pyroxenes selected by Cameronand Papike (1981), resent the real numbers of Na and R3* at the M sites. for which the Q values are less than 1.90 and Mn is less However, substitution 3 (e.g.,Al-Al) works to move the than 0.08 atoms per formula units, are plotted inthe Q-J J and, Q values closer to the origin of the Q-J diagram, diagram of Figure 3. The "CaMgTAL" pyroxene (Cam- and substitution 2 (e.g., Na-Tio') to move the ,I value eron and Papike, l98l) is included in the Quad area as farther away from the Q axis ofordinates. Therefore, the described later in this report (Table 3, no. l). Only 20 effectsof substitutions 2 and 3 tend to cancel each other analyses among 406 plot slightly over the line Q + J : out in and near the area of the Na pyroxenes.Thus the "/ 2.0, and most of these show unusual total numbers of (: 2Na) values in the Na-rich pyroxenes represent,to a cations. The results ofthe classificationofthe pyroxenes good approximation, the total number of Na and R3' (A1, into the four chemical groups by this procedure are in Fe3*,Cr3*, and Sc3*)at the M sites. almost complete agreementwith the results obtained by The boundary Q + J: 2.0 representsthe upper limit Deer et al. (1978)and by Cameronand Papike(1981). A of Q + J ar the M sites. The boundary Q + J : 1.5 few unusual pyroxeneswith Mn less than 0.08 atoms for representsthe limit below which more than half of the the chemical formula unit have been found to lie outside : Ml or M2 sites may be occupied by ions other than Q the areabetween the lines Q + J: 2.0 and Q + J 1.5 and ,I ions. In this case,the pyroxenesare consideredas n the Q-J diagram. The classification of these unusual belonging to Others, which include the Mn-Mg and Li pyroxeneswill be discussedlater in this report. pyroxenes,johannsenite, petedunnite, and esseneite. The pyroxenesthat plot in the area between Q + J: Equations 3 and 4 represent the lines dividing the area 2.0 and Q + J : 1.5have components than Qand,Iions limited by the two above-mentioned Q + "Ilines into Ca at lessthan 25o/oof the M sites.Therefore. we can classify I 128 MORIMOTO:NOMENCLATURE OF PYROXENES

TABLE3. Chemicalcomposition and classification of eight unusual pyroxenes

A. Ca-rich group related to S3 and S4 B. Na-richgroup related to S2 1: 320-8 7:492-19 (406-16) 2:403-3 3: D andS- 4: T andR-- 5: 488-9 6:491-14 C andGf 8: C andG{ Si 1.443 1.506 1.434 1.196 1.994 2.024 2.026 2.00 2.00 2.00 2.00 2.00 2.02 2.03 2.01 AI o.577 0.494 0.566 0.804 0.032 0.000 0.000 0.000 AI 0.091 0.'t71 0.306 0.186 0.000 0.021 0.098 0.348 Ti.* 0.165 0.065 0.o22 0.111 0.265 0.023 0.227 0.104 Ti0* 0.394 Fe3* 0.128 0.159 0.218 0.458 o.728 0.192 0.031 Mg 0.385 0.570 0.408 0.289 0.150 0.070 0.070 0.168 Fee+ 0.2292.00 0.0632.02 0.0602.00 2.00 0.1072.00 0.113 2.00 0.4201.98 0.3562.00 Mn 0.005 0.007 0.005 0.003 0.006 0.021 0.011 0.992 0.975 0.979 1.021 0.083 0.155 0.152 0.361 Na 0.006 0.007 0.002 0.933 0.872 0.794 0.610 K 0.000 0.001 0.009 0.006 1.61 1.61 1.45 1.31 0.34 0.34 0.64 '1.87 0.89 0.01 0.01 0.00 0.00 1.74 1.59 1.22 Mineral subsilicictitanian subsilicic subsilicic subsilicicti- titanian calcian fer- titanian aegirine- titanianfer- names ferrian diop- aluminian aluminian tanoan magnesran roan ae- augite roanom- side ferrian ferrian aluminian ferroan ae- girine phacite diopside diopside pyroxene gtnne Namesin titanaugite(320- fassaite fassaite titanaugite titanianaegir- aegirine- titanian aegirine- titanianferro- literature 8) ine augite augite (492- omphacite fassaite 19) (406_16) titanian aegirine CaM9TAL(C (c and G)t and P)t

Nofe.'Numbers such as 320-8, etc. represent pages and analysis number in Deer et al. (1978).Other referencesare in text. With the exception of 320-8(:406-16), all the Deeret al. (1978)analyses in this table were not includedin the 103 selectedanalyses of Cameronand Papike(1981). Atl pyroxenes in the table are shown with their numbers in the O-Jdiagram (Fig. 7). S2, 53, and S4 represent the following components of substitutions 2, 3, and 4, respectively:52 : NaRAjTi6.tSi,O.,S3 : CaR3*AlSiOu,and 54 : CaRAITiS.gAlSiOu.To indicate R ions explicitly in these components,the notation S(R), such as S2(Mg) and S3(AD,is used. S3(Fe)is a new pyroxene,esseneite (Es). Component ratios for the eight samples are as tottows: ('1)lWgiel':fq'o)nos4(Mg)"s4(Fe)16Es13S3(Al),, (2) (wo.uEn,5Fsr)5sS3(Al)r7Es16S4(Mg),,s4(FeL,(3) (wo..En.oFs.)..S3(At).,Es,,S4(Mg)0, (j) S3(TD""S4(Mo).r(wo',Fsr)aS3(Al),.,(5) AeouS2(Mg)".S2(Fe),0^6,(6) (AeTaJd,wo6Fs6Eni*S2.a., (7) (Ae,eJd,oFs,,wo"En,)r,S2(Fe)*s2(l\4g).a", (8) (Jd..Ae"Wo'.Fs15En7D6S2(Fe)1rS2(Mg)r4..The symbol a representsminor components,some of which have unusuafmetal Aiios ior ini pyroiene structure. * Devineand Sigurdsson(1980), Table 1 for fassaite. 't Tracy and Robinson(1977), Table 3, analysis I for pyroxene from the Allende meteorite(Mason, 1974). t Cameronand Papike(1981), Tabte A3, anatysis920-8 and 406-16. + Curtisand Gittins(1979), Table 2, analysis5 for no. 7 and TabteS, anatysis5 for no. 8. such pyroxenes on the basis of the normalized Q and J nopyroxenes,which have wide rangesof chemical com- components, thereby neglecting the effects of the other position. Therefore, the Ca-Mg-Fe pyroxenesare defined components. The following procedures are adopted for on the basisof symmetry and relative amountsof CarSirO. further classification:(l) The pyroxenesin the Quad area (Wo), MgrSirOu(En), and Fe!*SirO. (Fs). The composi- are classified on the pyroxene quadrilateral Wo-En-Fs tion rangesofthe clinopyroxenesand orthopyroxenesare diagram with normalized Ca, Mg, and >Fe (: psz++ Fe3* indicated in Figures4 and 5, respectively,where the com- + Mn) atoms. (2) The pyroxenesin the Na area are jad- position is normalized to Ca * Mg + ZFe : 100 with eite, aegirine, kosmochlor, and jervisite. Becausekos- )pg : pgz++ Fe3*+ Mn2+.r0 mochlor and jervisite show little or no solid solution to- r0 pyroxenes, ward other end members, they play no role in the For the nomenclature of the Ca-Mg-Fe normal- ization must be made to Ca * Mg + ZFe : 100, where )Fe : classification. Jadeite and aegirine are classified on the Fe2* * Fe3++ Mn. Hereafter the mole percentof the end mem- Quad-Jd-Ae diagram togetherwith the Ca-Na pyroxenes, ber components is always used without remark and is repre- aegirine-augiteand omphacite. sentedsimply by o/0.If the mole percentsof quadrilateral com- 66quadrilateral" ponents are calculatedby the atomic percent ofCa to the total Classificationof the Ca-Mg-Fe pyroxenes cations at the M sites, no pyroxenesshould contain more than The common rock-forming pyroxenes form wide ranges 50o/oCarSizOu. However, if Ca, Mg, and Fe are normalized, or calculatedas 100Ca,u(Ca+ Mg + >Fe), 100 Me/(Ca + Mg + of solid pyroxenes solutions of the Ca-Mg-Fe and can be )Fe), and 100 ZFel(Ca + Mg + )Fe), respectively,then some expressedby the pyroxene quadrilateral of the MgrSirO. will plot on a Wo-En-Fs triangular diagram above the (EnlFel-SirOu @spaMgsiro6 (DiFCaFer*SirO6 (Hd) 50o/oCa,Si,Ou line. Especiallywhen the plot in the Q-J diagnm system. The Ca-Mg-Fe pyroxenes include varieties that is very close to or outside of the boundary Q + t : 1.5, the petedunnite have orthorhombic symmetry. These orthopyroxenes effectofjohannsenite and componentsmust be con- sidered.Ifthe effect is negligible,the pyroxene must be consid- consist essentially of a simple chemical series ered to have an unusual composition and must be referred to (Mg,Fe)rSirO6and thus contrast with the Ca-Mg-Fe cli- the section ofunusual pyroxenes. MORIMOTO:NOMENCLATURE OF PYROXENES rr29

Co rSirO,( Wo)

diopside lhedenbergite \ \ ou9ite c2/ c \

pigeonite \ P 27/c clinoenstotite I clinoferrositite \ 50 M92Si205(En) FerSirO5(Fs) Fig. 4. Composition rangesof the Ca-Mg-Fe clinopyroxeneswith acceptednames.

The distinction betweenaugite and pigeonite in the Ca- jervisite, these two speciesare separatelytreated in the Mg-Fe pyroxenesis primarily structural, their spacegroups classification of the Na pyroxenes.Both jadeite and ae- being C2/c and.P2,/c, respectively.There is a miscibility girine, however, show extensive solid solution with the gap between augite and pigeonite, and many pyroxenes Ca-Mg-Fe pyroxenes, especially with the diopside-hed- with I 5-250/oWo have proved to be mixtures of the two. enbergiteseries and augite, leading to the Ca-Na pyrox- Augite with less than about 250loWo is often called sub- enes.The Na and Ca-Na pyroxenesare classifiedon the calcic augite.On heating,pigeonite undergoes a rapid dis- Quad-Jd-Ae diagram (Fie. 6) with normalized Q (Wo + placive transformationlo a C2/c structure, which cannot En * Fs), Jd, and Ae components." The arbitrary divi- be quenched.Augite does not show this type oftransfor- mation. ttTo normalize Q, Jd, and Ae components,the sum of Ca + The most Ca-rich orthopyroxene contains approxi- Mg + Fe2* + 2Na at the M sites must be made to total 100%. mately 50/oWo. The high-temperature form of enstatite Then the normalized percentageof 2Na must be divided into has the spacegroup Pbcn and can be expressedas "en- the ratio of AVFe3* to give the ratio of Jd/Ae. Thus Q + Jd + Ae must always give 1000/0.When the plot in the diagram statite-Pbcn." This form is not quenchable and has not Q-J is significantly outside the boundary Q + J :2.0, the effect of been found in nature. "Protoenstatite" has been used substitution 2 must be considered,as in the section ofunusual conventionally to describethis form, but this name is not pyroxenes. adopted as a mineral name. The Wo value of "enstatite- Pbcn" doesnot exceed2o/o, and the En value commonly Q (Wo,En, Fs) exceeds900/0. Thus the composition field of "enstatite- Pbcn" is different from that of enstatite-Pbca. /" Classification of the Na and Ca-Na pyroxenes "\ The Na pyroxenes, jadeite and aegirine, commonly contain more than 900/oof the NaAlSirO6 or NaFe3*Si2O6 component, respectively,but contain neither the Ko nor the Je component. Becausekosmochlor is a rare acces- sory constituent of some iron meteorites and only one omphocite o€irine-q€ite terrestrial locality is known for each of kosmochlor and

iodeite qegirine \

50 MgzSi?06(En) Fe?Si,O6(Fs) NoAlSi2 Og (Jd ) NoFe3'si2o5(Ae) Fig. 5. Composition rangesoforthopyroxenes with accepted Fig. 6. Ca-Mg-Fe and Na pyroxenes with acceptednames. names. Quad represents the Ca-Mg-Fe pyroxene area (see Fig. 4). l 130 MORIMOTO:NOMENCLATURE OF PYROXENES

Tnaue5. List of adjectivalmodifiers to be usedfor pyroxene mineralnames

Content" Name

Al3+ >0.10 aluminian Ca2* >0.10 calcian Cre* >0.01 chromian Fe2* >0.10 ferroan Fe"' >0.10 ferrian Li* >0.01 lithian Mg* >0.10 magnesran Mn,* >0.10 manganoan Mns+ >0.01 manganran >0.10 sodian Fig. 7. diagramfor eight unusualpyroxenes with value Nat Q-l Q Ni2+ >0.01 nickeloan less than 1.62 and Mn less than 0.08 atoms per formula unit si.* <1.75 subsilicic (Table 3). The components formed by the substitutions I to 4, Ti3* >0.01 titanoan as indicated in Table l, are plotted in the diagram. They repre- Ti4* >0.10 titanian >0.01 zrncran sent the following compositions: Sl : NaR3*SirO6, 52 : Zn2+ NaRfrjTiijSi,O", 53 : CaR3*AlSiOu,and 54 : CaRijTiSjAl- Note.'The limit of the content is based on the values listed in Table 4. sio,. * Numberof cationsper formulaunit M2M1TrO6.lf the mineralname itself impliesthe presenceot certain cations, adiectivalmodifiers for these cations should not be used ("subsilicic" is an exception). sions between the Ca-Mg-Fe pyroxenes, Na-Ca pyrox- enes,and Na pyroxenes are defined at 20o/oand 80o/oof 0. Omphacite displays a C2/c = P2/n polymorphic tran- occur with the P2/n structwe. The classification of the sition, and both high-temperatureC2/c and low-temper- Ca-Na pyroxenes by Esseneand Fyfe (1967) is not fol- atureP2/n polymorphs appear in nature. Omphacite can lowed in this report. thus be divided into two subspecies:omphacite-C2/c and omphacite-P2/n. Becauseomphacite-P2/n shows a unique Classification of other pyroxenes different from that ofjadeite and augite, Most naturally occurring pyroxenes in the Others area it is acceptedas an independentpyroxene species.Aegir- are johannsenite (CaMnSirO.), petedunnite (CaZnSirOr), ine-augite is also acceptedas an independent speciesto and spodumene (LiAlSirOu) (Fig. 2). Recent investiga- keep balance with omphacite, though it is not known to tions of natural Mn-bearing pyroxeneshave yielded two new minerals, kanoite and its dimorph donpeacorite, TneLe4. Extremechemical compositions of pyroxenesin Deer (Mn,Mg)MgSirOu, which seem to form a solid solution (1978) et al. with En (Peterson et al., 1984). They too occur in the Mg-Fe Others area. These results suggesta possible Mn-Mg-Fe pyroxenes Ca pyroxenes Na pyroxenes pyroxene quadrilateral. Esseneite(CaFe3*AlSiOu) is the Si 1.76(42-91 1.44 (320-8r 1.94(488-9) first pyroxene with the substitution 3 as describedin Ta- A13* o.24(42-9) 0.56 (320-8) 0.07(488-8) ble l. Fes* 0.04(49-8) 0.09 (320-11) 0.02(488-9) Al3* 0.15(49-6) 0.35 (320-11) 0.98(464-1 ) Ti1* 0.04(40-30) 0.17 (320-8)8 0.27(488-9)c Classification of unusual pyroxenes Fe3+ (170-8) (321-5)D 0.s7(487-1) 0.12 0.37 pyroxeneswith unusual chemical compositions Mgz* 1.99 (41-1) 1.27 (208-4) 0.15 (488-9) Several 't.72(47-33)E Fe'?* 1.09 (220-13) 0.11(488-9) (Table 3) appear outside the area between the lines Q + Mn2* 0.27(45-21)F 0.36 (217-5)G 0.03(487-4) J : 2.0 and + J : 1.5 in the though they (36-9) (207-11) Q Q-,Idiagram, Ct2* 0.02 0.06 pyroxenes Ni2* 0.003(31 7-1) do not belong in the area of Other mentioned Zn2+ 0.21 (216-11)' above (Fig. 7). They contain large amounts of chemical Ca2* 0.26(1 69-2) 1.O3 (202-4l. 0.16 (466-14) components involved in substitutions 2, 3, and 4 men- Na* 0.10 (169-2) 0.31 (323-7) 0.98(464-1) tioned in Table l. Note.'Givenare the numberof cationsoer tormula unit. minimum values These pyroxenescan be divided into two groups: first, for Si, and maximum values for other cations. Bold numbers are for the mainconstituent elements. Numbers in the oarenthesessuch as 42-9, etc., Ca-rich pyroxenes with CaR3*AlSiO6(S3, Fig. 7) and indicatepages and analysisnumbers in Deeret al. (1978). Other references CaRtlTifi.lAlsio6 (S4, Fig. 7) components representing are in text. substitutions 3 and 4, respectively,and second,Na-rich a Table 3, no. 1; Table 3, no. 4: Pyroxene from the Allende meteorite 1.20 (Mason,1974; Tracy and Robinson,1 977). pyroxenes with the NaKjTi6jSirO. component repre- 6 Probe analyses0.252 and 0.282, halt ol CaRAITidjAlSiO6(S4) Crracy senting substitution 2 (52, Fig. 7). The former shows a and Robinson,1977; Robinson,1980). c Table3, no. 5. Halfof NaR6:Ti63SirO6(S2). significant deficiencyof Si atoms such as Si < 1.60 in the D406-150.67, omitted because of possibleerrors in chemicalanalysis. standard formula resulting in the value closeto or less EProbe O analysis1.880 (Jaffe et al., 1978). than 1.5 (S4, Fig. 7). The latter appearsoutside the line FProbe analysis 0.301 (Robinson, 1 980), kanoite 1.04 (Kobayashi,1 977). c Johannsenite0.963 (41 7-2). Q + J : 2.0 approachingpoint 52 in Figure 7. All these HKosmochlor 0.90 (522-1). unusual pyroxenes are classified by using the accepted 'Petedunnite (Table 0.37 2, footnote with asterisk). pyroxene names and the adjectival modifiers mentioned MORIMOTO:NOMENCLATURE OF PYROXENES I l3l

TraLe6. Obsoletepyroxene names Teew d-Continued acmite: aegirine picrophyff= altered pyroxendl aegirite(aegyrite) : aegirine pigeonite-augite: probably subcalcicaugife aegerine-hedenberyile: augite pitkarantite : pyroxene? agalite : probably enstatitepaftly altered to potash-aegirine: synthetic product, probably not properly characterized agfaite = alteted spoclumene protheite : augite alalite: diopside protobastite : enstatite afkali augite : aegirine-augite pyraffolite: altered pyroxene?, talc? ambfystegite: enstatite pyrgom: pytoxene anthochroite: augite sahfite = diopside asteroite : iron-rich(or Fe-rich)augife salite : diopsde baikalite : diopside schefferite: manganoandiopside bastite : enstatite that has altered to serpentine,talc, or perhaps antho- schillerspar(schillerspat) : enstafite that is altered to serpentine,talc, or phyllite blanfordite: manganoanaegirine-augite shepardite: enstatite bronzite: enstatite soda-spodumene: sodian spodumene calc-cfinobronzite: pigeonite strakonitzite : altered pyroxene, steatite? calc-cfinoenstatite : pigeonite szaboite : partly altered enstatite calc-cfinohypersthene : pigeonite titanaugite : titanian augite calc-pigeonite= subcalcic auglte titandiopside: titanian diopside canaanite: diopside titanpigeonite= titanian pigeonite chfadnite: enstatite trachyaugite: augite chforomelanite: omphaciteor aegirine-augite traversellite: dioDside chrome-acmite : chromian aegirine triphane: spodumene chromejadeite : chromia jadeite tuxtlite = omphacite clinohypersthene : clinoenstatite ot clinoferrosilite uralite: pseudomorphof amphiboleafter pyroxenes coccolite (kokkolith) : iron-rich(or Fe-rich)augite urbanite : iron-rich (or Fe-rich) augite ot aegirine-augite cymatofite: altered spodumene ureyite: kosmochlor diaclasite: altered enstatite vanadinaugite: -bearing(or V-bearing)augife diallage = diopsidelhal has altered or that has good (100) parting; also vanadinbronzite: vanadium-bearing(or V-bearing)enstatite used tor alteration products of other pyroxenes vargasite = altered pyroxene? diopsidjadeite: omphacite victorite: enstatite endiopside: -rich(or Mg-rich) augite violaite: augite enstatite-diopside: magnesium-rich(or Mg-rich) augite viofan : magnesium-rich(or Mg+ichl augite or dipside eulite: ferrosilite eulysite : ferrosilite /VotejThe above pyroxene mineralnames, or namesthat refer to altered fassaite : ferrian aluminiandiopside or augite pyroxenes, have been formally discarded by the CNMMN. The correct fedorovite = diopside names are italicized.The originalform of this table was compiled by Mal- ferroaugite: augite colm Ross usingthe followingreferences: Dana (1 892); Tschermak(1 897); ferrohedenbergite: augite Chester(1886); Ford (1932);Winchell and Winchell(1951); Deer et al. ferrohypersthene: fenosilite (1963,1978); Strunz (1970); and the unpublishedThesaurus of Mineral- ferro-iohannsenite: iron-rich(or Fe-richljohannsenite ogicalTerms of the InternationalMineralogical Association, which has been ferropigeonite: iron-rich(or Fe-rich)pigeonite availablesince August 1974. ferrosalite : hedenbergite ficinite: enstatite funkite = hedenbergite germarite : altered enstatite below, exceptthe Allende pyroxene(Table 3, no. 4), which hiddenite: spodumene is called subsilicic titanoan aluminian pyroxene. : hudsonite hedenbergite The Allende pyroxene(no. 4) contains390/o of the S3(Ti) hypersthene = enstatite ot terrosilite jadeite-aegirine0adeite-aegirite) : jadeite ot aegirine (for notation, see note in Table 3) component : zincian manganoandiopside or augite CaR3*AlSiO6,where R3+: Ti, and can be consideredas killinite: alleted spodumene korea-augite: augite a new mineral. However, we have decided only to use kunzite: spodumene the acceptednames in this report and ifa specieshas not favroftite : diopside yet been approved, w€ use "pyroxene" as for no. 4 in favrovite = diopside fawrowite = diopside Table 3. The names used in literature for the unusual feucaugite: diopside pyroxenesare listed in Table 3 in comparison with those lime-bronzite : pyobably pqeonite or enstatite plus augite ("inverted" in report. The "CaMgTAL" pyroxene (no. l) is pigeonite) this loganite: diopside + + talc "diopside" in this classification. lotalite = hedenbergite : mafacolite diopside with good (001) parting, also diopside from Sala, MoDTFTERS Sweden Anrucrrvll mansjoite : augiteot diopsideot hedenbergite Adjectival modifiers for mineral names are used to in- mayaite: omphacite mellcrite: ofthopyroxene dicate unusual amounts of chemical constituents. In or- mondradite: probably an altered pyroxene der to define the unusual amounts for the pyroxene min- mussite: d,psde eral group quantitatively, extreme compositions of orthobronzite= enstatite orthoenstatite : enstatite pyroxeneshave been listed in Table 4, where the values orthoeulite : ferrosilite for the main cations are shown as well as those for the : orthoferrosilite ferrosilite qrtions. (1978) (1980) orthohypersthene = enstatite ot ferrosilite accessory Deeret al. and Robinson's paufite = enstatite table were mainly used in constructing Table 4. peckhamite: enstatite An element specified as a modifier should be present phastine : altered enstatite as a generalrule in a quantity larger than 0.1 atoms (or rr32 MORIMOTO:NOMENCLATURE OF PYROXENES

0.01 for lessabundant elements)in the standardchemical Rrrnnnucrs crrED formula of 6 oxygensor 4 metal atoms (Table 5) depend- Bailey, S.W. (1977) Report of the IMA-IUCr joint committee on nomen- ing on the maximum content in Table 4. clature. American Mineralogist, 62, 41 1415. The sufrxes are those proposedby Schaller(1930) and Bokij, G.B., and Ginzburg, J.V. (1985)The systematicsof mineral species adaptedby GNMMN (Nickel and Mandarino, 1987).The in pyroxenefamily. Trudy Instituta Geologii i Geofiziki (Novosibirsk), suffix "-ian" is used for the higher valence state (e.9., 610, 12-35. Cameron, M. and Papike, J.J. (1981) Structural and chemical variations ferrian) or for an element with a nonvariable state (e.g., in pyroxenes.American Mineralogist, 66, 1-50. lithian). The suffix "-oan" implies the lower valencestate Chester,A.H. (1886) Catalogueof minerals. John Wiley and Sons,N.Y. (e.g., ferroan). It is recommended that such modifiers Cosca,M.A., and Peacor,D.R. (1987) Chemistry and structureof essene- never be used for main cations normally contained in the ite (CaFe3*AlSiOu),a new pyroxene produced by pyrometamorphism. American Mineralogist, 72, 148-156. named mineral, for example, in terms like "calcian au- Curtis, L.W., and Gittins, l. (1979) Aluminous and titaniferous clinopy- gite," "aluminian omphacite," and "sodian aegirine-au- roxenesfrom regionally metamorphosedagpaitic rocks in central Lab- gite," in which the modifiers are obviously superfluous. rador.Journal ofPetrology, 20, 165-186. If there is less than the amount necessaryfor the as- Dana, E.S. (1892) The system of mineralogy (6th edition). Wiley, New signment of the modifiers such as "aluminian" in Table York. Deer, W.A., Howie, R.A., and Zussman, J. (1963) Rock-forming min- 5, or <0.1 Al, but if the increasedcontent of the element erals,vol. 2, Single-chainsilicates (first edition). I-ongman, Green and must be stressed,a modifier "Al-bearing" may be used. Co. Ltd., London. This second type of modifier should be used also (l) if - (1978) Rock-forming minerals,vol. 2A, Single-chainsilicates (2nd only an incomplete analysis is available, preventing the edition). Longman, U.K. and Wiley, New York. DeVine, J.D., and Sigurdsson,H. (1980)Gamet-fassaite calc- nod- calculation of a full chemical formula, or (2) for pyrox- ule from La Soufriere,St. Vincent. American Mineralogist, 65,302- eneswhere the valencestate of a cation is unknown. With 305. regard to the Si content in pyroxenes,it is suggestedthat Dowty, E. and Clark, J.R. (1973) Crystal structurerefinement and optical Si < 1.75 is a suitable limit for use of the term "subsili- propertiesof a'Ti3* fassaitefrom the Allende meteorite.American Min- cic," though one should bear in mind that the limit of Si eralogist, 58, 230-240. Essene,E.J., and Fyfe, W.S. (1967) Omphacitein California metamorphic < 5.75 for "subsilicic" in amphiboles correspondsto Si rocks. Contributions to Mineralogy and Petrology,15, l-23. < 1.5 for pyroxenes. Essene,E.J., and Peacor, D.R. (1987) Petedunnite (CaZnSirOu),a new In certain cases,particularly for the augite series,it is clinopyroxenefrom Franklin, New Jersey,and phaseequilibria for -166. convenient to use the following adjectival modifiers: Fe- zincian plroxenes. American Mineralogist, 72, 157 Ford, W.E. (1932) A textbook of mineralogy. Wiley, New York. rich, Mg-rich, and subcalcic. A prefix actually attached Jaffe,H.W., Jaffe,E.8., and Tracy, R.J. (1978) Orthoferrosilite and other or hyphenated to a mineral name, however, is incorrect iron-rich pyroxenesin microperthite gneissof the Mount Marcy area, and should be avoided (Nickel and Mandarino, 1987), Mountains. American Mineralogist, 63, I l6-136. becauseit would causethe mineral to be indexed alpha- Kobayashi, H. (1977)Kanoite, (Mn'z.Mg),[Si,Ou],a new clinoplnoxenein betically under the prefix rather than under the proper the from Tatehira, Oshima Peninsula, Hokkaido, Japan.Journal ofthe Geological SocietyofJapan, 83,537-542. mineral name. This is why such terms as "ferropigeon- I-eake, B.E., and Winchell, H. (1978) Nomenclature of . ite," "ferro-augite," etc., should not be used as mineral American Mineralogist, 63, 1023-1052. names. Mason, B. (1974) Aluminum-titanium-rich pyroxenes,with special ref- It is often useful to give the spacegroup of the mineral, erence to the Allende meteorite. American Mineralogist, 59, 1198- particularly 1202. when it can occur in two or more forms. For Mellini, M., Merlino, S., Orlandi, P., and Rinaldi, R. (1982) Cascadite example, we could distinguish between the two forms of andjervisite, two new scandiumsilicates from Baveno,Italy. American omphacite by adding the space-groupsymbol., i.e., om- Mineralogist, 67, 599-603. phacite-C2/c vs. omphacite-P2/n, or by adding the lat- Morimoto, N., and Kitamura, M. (1983) Q-J diagram for classification tice-type symbol, i.e., omphacite-C vs. omphacite-P (Bai- of pyroxenes.Journal of the JapaneseAssociation of Mineralogists, Economic Geologists,78, 141 (in ley, 1977). Petrologistsand Japanese). Nickel, E.H., and Mandarino, J.A. (1987) Proceduresinvolving the IMA Commission on New Minerals and Mineral Names and guidelineson Onsolrrn PYRoxENENAMES mineral nomenclature.Canadian Mineralogist, 25, 353-377; American Mineralogist, 72, 103l-1042. The namesof 105 pyroxenesor alteredpyroxenes listed Papike,J.J., Ed. (1969)Pyroxenes and amphiboles:Crystal chemistry and in Table 6 have formally been discardedby the CNMMN phasepetrology. Mineralogical Society ofAmerica SpecialPapet 2. and are therefore obsolete. The preferred name is itali- Peterson, E.U., Anovitz, L.M., and Essene,E.J (1984) Donpeacorite, cized in the same table. (Mn,Mg)MgSLOr, a n€w orthopyroxene and its proposed phase rela- tions in the system MnSiOj-MgSiOr-FeSiOr. American Mineralogist, 69,472480. AcxNowr-rncMENTs Prewitt, C.T., Ed. (1980) Reviewsin mineralogy,vol. 7. Pyroxenes.Min- We are thankful to ProfessorJ.H.D. Donnay, McGill University, Mon- eralogicalSociety of America, Washington,D.C. treal, who contributed greatly to the improvement of the report by his Robinson, P. (1980) The composition space of terrestrial pyroxenes- careful review. We also appreciatecriticisms and comments by Dr. A. Internal and externallimits. Mineralogical Societyof America Reviews Kato, National ScienceMuseum, Tokyo, Dr. M. Kitamura, Kyoto Uni- in Mineralogy, 7, 419494. versity, Kyoto, and the memben of the Commission on New Minerals Schaller, W.T. (1930) Adjectival endings of chemical elements used as and Mineral Names, IMA. modifiers to mineral names.American Mineralogist, 15,566-574. MORIMOTO: NOMENCLATUREOF PYROXENES l 133

Strunz, H. (1970) MineralogischeTabellen, 5 Auflage.Akademische Ver- Fen*from microprobe analyses.Neues Jahrbuch .fiir Mineralogie Mo- lagsgesellschaftGeest and Portig K.-G., Leipzig. narshefte,71-83. Tracy, R.J., and Robinson, P. (1977)Znnallitanian augitein alkali Winchell, A.N., and Winchell, H. (1951) Elementsof . from Tahiti and the nature of titanium substitutions in augite. Wiley, New York. American Mineralogist, 62, 634-645, Tschermak,G. (1897) khrbuch der Mineralogie. Alfred Holder, Wien. Vieten,K.andHamm,H.M.(1978)Additionalnotes"Onthecalculation MeruscnnrREcErvEDMencsT, 1988 of the crystal chemical formula of clinopyroxenes and their contents of MAr*uscx.rpr lccsprED Mav 6, 1988