ON the VATIDITY of CALDERITE PETEJ. DUNN Department Ol

Canadian Mineralogist Vol. 17, pp.569-571 (1979)

ON THE VATIDITY OF CALDERITE

PETEJ. DUNN Department ol Mineral Sciences,Srnithsonian Institution, Washington, D.C. 20560, USJ.

Ansrnacr A second occurrence of calderite was noted by de Villiers (1951), and the rnaterial was A garnet sample from Otjosondu, Namibia subsequently re-examined by Vermass (1952). (Soutlwest Africa) is re-examinedand found to In a third description, Klein (1966) described contain -50 mol. Vo of the calderite component. some calderitesfrom the WabuShiron formation The new data support older investigationsand- in southwestern- -.-;:- - - Labrador. In spite of these ideallv establish the legitimacy of calderite, ;- , , in MngFes+g(Sioa)r,as a speciesof the garnetgroupv. descriptio-ns'calderite remains unrecognized rhe ramiie stue'ieah^;li3ii1E,";;1.Fi;6; most reference works as a legitimate end- and D(obs.) 4.05 s/cms, Microprobeanalysis yields member of the garnet group. ths empirical formula (Mns.ssCas.re):u.rr(Fet*r.o, Alr.zaMgo.rgTio.os)s.0?(Si6.04Alo.ou) O-. Tbe oxidation staiJ of iiie f.;;;; iatiutiiea io tit ttr" valence Cnnnrsrnv requirements of garnets. Ct is proposed as an acronym for calderite. The sample studied was analyzed with an ARL-SEMQ electron microprobe using an oper- ating voltage of 15 kV and a beam current of SoMrvrerns 0.15 pA. The data were corrected for back- ground, backscatter absorption and fluorescence r6examen, un 6chantillon de grenat de Au used were Otjosondu (Namibie) s'avbrecontenir -5OVo (mol.) using Bence-Albee factors. Standards du p6le calddrite [ct: MngFes+r(SiOo)r],dont la a magnesian ferroan grossular for alu'minum validit6 commo membre de la famille des grenaJs and silicon, manganite for manganese, horn- est confinnde.Les mesuresdonnent a 11.81(1)A, blende for magnesium, calcium, iron and ti- no 1,875(2) et Do6 4.05.L'analyse i la microsonde tanium, and chromite for chromium. The re- (Mn3.e2Ca2.1s)16.11 conduit i Ia formule empirique sultant analysis is presented in Table 1. Iron (Foe+g.ozAlr.zaMgo.rsTi0.0Jrs.e?(Si6.erAlo.oo)Oaa. Le fer determined as total iron, and the oxidation est cotnme ferrique pour satisfaire b was consid6r6 to fit the f6quilibre des charges. state of the iron was calculated (Traduit par la R6daction) known valence requirements of garnets, using tle deficiency of aluminum as an indicator of the amount of iron present in the ferriq state. INtnooucnoN Examination and analysis of a number of specimens labeled calderite in the Smithsonian The name calderite was first given to a collections and the collections of the British "siliceo iron and manganese rock" from Kat- Museum (N. H.) indicated that most of these kamsandi, northwest of Hazaribagh, in what is specimensare ferroan and magnesianandradites. now the state of Bihar in western India, by ar" hosts for abundant inclusions of fer' Piddington (1851). The analysiswas likely faulty They roan diopside and magnesian hedenbergite, and it was recognized as that of a garnet by which likely contributed to incorrect wet-chem- Blandford & Siichting (1857). Calderite remained ical analyses. poorly defined for some years and was used by Mallet (1887) to describeboth a "manganese- iron garnet" and a common andradite. In 19O9 Drscussloll Fermor formally applied the name calderite to the theoretical end-member Mn"Fe'+r(SiOn)g, Only one of the specimensstudied, BM 1951- germane which is the manganese analog of andradite, 21 from Otjosondu, Namibia, is to 'manganese Ca'Fee+r(SiOo)r, atd the ferric iron analog of this discussion because of its high spessartine, Mn'Alr(SiOn)'. This nomenclature and iron sontent. The sample is dark reddish w:rs continued by Fermor (1927) in his investi- brown, with many stringers of pyrolusite and gation of some Indian garnets. other manganese oxides, and is che'mically 569

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for the end-member, MngFes+:(SiOa)s.The ob- TABLEI. CHEMICALA}IALYSES OF CALDERITE servations of Vermass (1,952) are confirmed; although l. 2. 3. 4. the composition of this garnet could be expressed as SpessartineuAndraditeseCalde- sl02 35.16 34.56 5.942 5.984 riten, this calculation only serves to point out Tl02 0.28 0.036 that this garnet cannot be assignedto the composition range garnet A1203 9.04 4.72 1.801 0.963 of the group without the presenceof tle calderite component. Fe203* 16.27 22.96 2.069 2.992 Considering that tfie calderite iomponent must Feo 0.00 0.000 be present, at least in part, to account for. the MgO 0.50 0.56 0.126 0.145 uncommon composition of this garnet, it is CaO 12.'|.2 14.60 2.195 2.709 much simpler to calculate the composition in ter.rnsof the three (cal- l.tno 27.38 22.12 3.919 3.244 dominant end-members derite, spessartineand grossular) as Calderiteot Totar T0T:75' ECSZ G r os s ul ar sa,Sp e s I el t in e Ls. The preceding data relate to the Otjosondu sample only. Klein (1966) published l. BMl95l-21, mlcroprobeanalysis. a description of calderite samples from the Wabush 2. Bl,ll95l-21 frrm Vemass(1952) , iron-formation in Labrador. His samples occur 3. numberof ions, basedon 24 oxygens,for #1. in two assemblages:(1) an aegirine-rhodonite- 4. numberof lons, basedon 24 oxygens,for #2. hematite-rhodochrosite assemblage,and (2) a Accuracy0f data for analysis #t :-ZgT amounT quartz-hematite-rhodon ite-kutnahorite-calderi te present. rock. Chemical analysesof.these samplesyielded (Mnr.'Cao.az)(Fes+r.oz) (SiOa)r.oo for sample(1) *- Iron deteminedas total iron andcalculated and (Mn,.aoCar.ru)(Fes+:.or) (SiOa)s.oo for sam- to flll deflciencyfor 3+ lons in the garnet ple (2). Klein's samples are very low in alumi- structure. num (less than 0.3Vo estimated). and are very clearly legitimate calderites and closer to the homogeneous. given This sample, to the British end-member composition than the aluminous (N. Museum H.) by de Villiers, is the same Otjosondu sample described here. sample analyzed. by C. F. J. de Walt in de In summary, calderite is a legitimate and Villiers (1951) and reanalyzed by Vermass valid end-member of the garnet group. Cr is (1952) as garnet his S1. proposed as an acronym for calderite inasmuch The physical determinations of the as the other possibilities,Ca, Cl, Cd, Ce and Cr, presentsrudy [a 11.81(1)A, no 1.875(2),D are all symbols of chemical elements. (obs.) 5.05 g/cm"l are in good agreementwith t!oe9 gf Vermass (1952) z a 11.8194, no I.872, D (obs.) 4.081 g/om0. Application of the AcKNowLEDGEMENTS Gladstone-Dale relationship (Mandarino L976) to this garnet .yields a Kc value of 0.215 de- The author is indebted to Drs. Joseph Manda- termined from the chernical analysis, compared rino, Michael Fleischer and Daniel Appleman with a Kp value of. 0.216 determined from for helpful discussionsand critical readings. physical properties. The compatibility index, (1.00G.KplKc) (Mandarino L979) is 0.005, indicating superior compatibility of the data. ReFsRBNcss An examination of the analysis of sample BM 1951-21 in Table 1 indicates it is slightly BLANDFoRD,M. & Sttctrrnq E. (1857): Ver- deficient in 3* ions. This deficiency may be handlungender Gesellschafl.Deut. Geol, Ges, due to experimental error or the presence of z. g, 4. some manganese as Mn8+. The empirical formula of this specimen, calculated on the basis on Vrrrrnng J.'8. (1951): The manganeseores of 24 oxygen atoms, is (Mna.erCa.:.rs)>r.rr(Fet+0.o, of Otjosondu,Southwest Africa. Geol. Soc.S. Afr. AL.zaMgo.rsTio.og) >g.er ( Sir.eaA'lo.* ) Ozl. The sample Trans, 54, 89-98. clearly doesnot fall within the composition range FERMo& L. L. (1909): The manganese-orede- of the recognizedgarnet species;it is a legitimate posits of India. I. Introduction and mineralogy. calderite and sonforms to the general formula Geol. Sum. Indio Mem. 87, 182-186.

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(1927)z On the composition of some (t979) z The Gladstone-Dale relationship. Indian garnets.Geol. Surv. India Rec, 59, L9I- III: Some general applications. Can. Mineral. 207. L7, 7t-76. KLETN,C., Jn. (1966): Mineralogy and petrology PropnqcroN, H. (1851)r On calderite, an un- of the metamorphosedWabush iron formation, described siliceo-iron-and-manganese-rock,from southwesternLabrador. J. Petrology 7, 246-305. the District of Burdwan. J. Asiatic Soc. Bengal 19, 145-148. (1887): A of the Geology Mar,r.rt, F. R. Manual (1952): Manganese-irongarnet of India. 4. Mineralogy. Geol. Surv. India, Cal- VnnrvrEss,F. H. S. South-West Africa. Mineral. cutta. from Otjosondu, Mag. 29, 946-95t. Maroeuxo, J. A, (1976): The Gladstone-Dale relationship. I: Derivation of new .constants. ReceivedDecernber 1978; revised manusctipt ac- Can. Mlneral. 14, 498-502. cepted May 1979.

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