American Mineralogist, Volume 65, pages 355-360, 1980

The stability of danalite, FeoBer(SiOr3S

DoNero M. Bunr Department of Geology, Arizona State University Tempe,Arizona 85281

Abstract

End-memberdanalite is compositionallyequivalent to a mixture of pyrrhotite, phenakite, and fayalite, but danalite's natural occurrenceswith , ,and suggest that it is stable under somewhat more sulfidizing conditions than pyrrhotite and more oxidiz- ing conditions than fayatte. Danalite tends not to occur with hematite. Thesefacts can be usedto constructa tentative log /",-log f o,diagtan for the stability of the end member. The diagram shows that danalite, if it is stable at all, has an extremely narrow stability field cen- tered near the pyrrhotite,/magnetitefield boundary. Outside this field, phenakite (or, at low temperatures,bertrandite) is stablewith magnetite,pyrrhotite (or pyrite), and quartz. A natu- ral example of theseequilibria apparently occurs at Mountain, Bartlett, New Hamp- shire, where zoned danalite-helvite solid solutions occur as overgrowths on phenakite with magnetite,pyrite, and quartz. Danalite is the only end memberof the helvite group that is appreciablysensitive to hypo- gene oxidation. The Mn and Zn end,members helvite and genthelviteare instead sensitive only to S-O exchange(variation in log /",//",).

Introduction 2 FeoBe,(SiOo)rS:2 FeS+ 3 Be,SiOo+ 3 FerSiOo Danalite, FeoBer(SiOo)rS,is a rare beryllium ore danalite: troilite * phenakite* fayalite mineral in iron-rich skarns,greisens, and related me- Troilite (Tr) is not a common terrestrial phase; for tasomaticrocks (Glasset al., 19441,Beus, 1966; Dunn, the purposesofthis discussionit can be replacedby 1976). lt typically contains considerable helvite, pyrrhotite, Fe,-,S. The non-stoichiometryof pyrrho- Mn Ber(SiOo)rS,or genthelvite,Zn Ber(SiOo)rS,i1 tite has been neglectedfor conveniencein balancing solid solution, and crystalsmay be distinctly zoned. reactions. The closestapproach to "danalite" in analyzednatu- The compositionalrelation expressedby the equa- ral specimensis 87 mole percentof the Fe end mem- tion is also shown in Figure l, a tentative depiction ber (Dunn, 1976).In a laboratory study (Mel?nikovet of mineral compatibilities in the reciprocal ternary al., 1968),danalite was the only end member of the system /Fe,Be/ /SiOo,S/ [or Fe"SiOo-2BeFe_,- helvite group that could not be synthesized. Sr(SiOr)-, in the "exchange operator" notation of The above data might suggestthat end-member Bvt, 19741.This systemis a subsystemof the four- danalite is unstable. This question cannot be an- component system FeO-BeO-SiOr-SO_r, itself a sweredwithout further experimentalwork; my objec- subsystemof the five-componentsystem Fe-Be-Si- tive is merely to examinethe reasonfor the rarity of O-S. Eight minerals in this system are listed in Ta- danalite-rich solutions in nature".The stabilities of ble l. helvite and genthelvite will be considered in later contributions. Incompatibilities The phase rule implies that not all eight of the Phases phasesin Table I can be compatibleat a given pres- Compositionally, end-memberdanalite is equiva- sure and temperature.Well-known incompatibilities lent to a mixture of troilite, phenakite, and fayalite, (unstable4ssemblages) in the Be.free subsystemFe- as shown by the following equation: Si-O-S include pyrrhotite-hematite, pyrite-fayalite, 0003-004x/80/0304-0355$02.00 356 BURT: STABILITY OF DANALITE

2FcS 2BeS and Tr ') ("ro 3Py+4Dan: l0Po+3Mt+6Phe +6Qtz (2) Hematite-danahteis not a well-documentedassem- tI blage, and the alternativeassemblage apparently oc- curs (Barton and Goldsmith, 1968,p. 59). Analogies 2S with other systemsalso suggestthat an FeO-rich 2S+5i04 mineral such as danalite will be incompatible with hematite.Reaction (l) hastherefore been assumedto go Foy to the right. Note, however, that Zubkov et al. terSiOO BerSiOO (1972,p.362-363) have reported a danalite with 5l atomic percent Fe end member Ssing altered by hematite, but it is not known if this representsan #----> equilibrium assemblage. Fig. |. Assumed mineral compatibilities in the reciprocal Reaction (2) is still more of a problem. The left as- ternary systemFe2SiOa-Be2SiOa-2FeS-2BeS (or Fe,Bel/SiOa,S). pyrite-danalite, The phases shown are probably compatible with quartz in the semblage, is relatively common, systemFeO-BeO-SiO2-SO_r. Abbreviations are given in Table I whereasthe right assemblageapparently has not yet and the text. beenreported. On the other hand, the danalite stabil- ity field in nature is undoubtedly extendedby solid and hematite-fayalite. Figure I implies that, if dan- solution of other components,and pyrrhotite-bearing alite is stable, pynhotite-fayalite-phenakite must assemblagesare rarely reported.Without experimen- also be an unstable assemblage.(Strictly speaking, tal data, then, the stable assemblagein this reaction due to the non-stoichiometryof pyrrhotite, this con- cannot be determined. clusion doesnot follow directly from Figure l. Nev- Stability diagrams ertheless,it can easily be shown that non-stoichio- Given the above data and assumptions,danalite metric pyrrhotite plus fayalite plus phenakite is has five possiblebreakdown reactionsinvolving Or, compositionally equivalent to the presumably more stable assemblagemagnetite-danalite-quartz.) Sr, and the phasesin Table l. These reactions are listed in Table 2 and are depicted on Figure 2, The phasesin Table 1, and the incompatibilities a schematic isobaric, isothermal log dia- mentioned above,can be used as input for computer /",-log .fo, gram. In view of the lack of thermochemicaland ex- program REACTTON(Finger and Burt, 1972),h order perimental data on the Be-bearingphases, the dia- to determineif there are other incompatibilities.Two gram is drawn at an arbitrary (moderate or low) reactionsthat are printed out are: pressureand temperature.The slopesof the lines on 6 Hem * 2Dan: Py + 6 Mt + 3 phe + etz (l) this diagram are fixed by compositionalrestrictions, and the topology should remain the same over a range of pressuresand temperatures (in Table l. Eight phasesin the systemFe-Be-Si-O-S the vicinity of 0.2-2.0kbar, 300-500'C). The reactionsinvolving the Be-freesubsystem Fe- Name Abbreviation Composition Si-O-S on Figure 2 are too well known to require Pyrrhotite Po cornment(Holland, 1965).Superimposed on theseis r-x a hypothetical danalite stability field, outlined with Pyrite Py FeS2 dark lines. The danalite stability field is seento be re- Magnetite Mt Ft3o4 stricted to the vicinity of the pyrrhotite/magnetite

Hematlte ftn F"203 field boundary. The assemblagedanalite-quartz is stableover the samearea as danalite alone,except at Fayallte Fay FerSiOO the lower left corner of the diagram. Danalite's com- Phenaki.te Phe BerSiOO patibility with pyrite is, as mentioned,uncertain, and the danalite stability field could be considerably Danalite Dan FeOBe,(SiOO) rS smaller than Figure 2 implies. (As mentioned in the Quart z Qtz sio2 introduction, end-member danalite could be un- stable.) BURT: STABILITY OF DANALITE 357

6(0

cl .: 3 o u (9

Fe

O2 Fig. 2. Hypothetical log .fs,-log 1o, diagram for danalite Figure 2, but in the presenceof a stability in the system Fe-Be-Si-O-S. The inset shows mineral Fig. 3. Diagram similar to fugacity of CO2, and showing hypothetical (schematic) compositions projected onto the composition plane Fe-Be-Si. The constant limits for danalite solid solutionsof 75 and 50 atomic Vo thicker lines outline the danalite stability field; the reactions stability assumes that the end-member danalite field involving danalite are listed in Table 2. Mineral abbreviations are Fe. This diagram (Dan,*) indicated on Figure 2. given in Table l. is more restricted than that Siderite stability is not considered. Danalite-rich solid solutions are common enough in nature, however,and their stabilitiescan similarly 2Dan+ 6 CO, : 6 Sid + 3 Phe+ 3 Qtz * 2 Po be depicted (Fig. 3). Figure 3 is analogousto Figure 2, exc,eptthat a small fugacity of CO, allows the In this regard, Palache(1907) reports the alteration graphite line to eclipse the fayatte stability field (cl of danalite in a cavity from Cape Ann, Mas- Holland, 1965).By analogywith other systems,solid sachusettsto a mixture of siderite,phenakite, quartz, solution of, e.g., helvite is shown as allowing the end- pyrite, and sphalerite, all coated by later kaolinite member danalite field (here shown as not touching and hematite. pynte) to expandconsiderably. Again due to the lack of data on danalite,the fields and numbersshown on Table 2. Five breakdown reactions of danaliter this diagram are purely hypothetical. Mhor sub- stitution of Mn in magnetitehas been neglected. The superpositionof a stability field for siderite (Sid) on Figure 3 has also been neglected.At low 1. 6 Dan * 4 Or= 2 Mt + 9 Fay + 9 Phe + 3 S, temperatures,with increasingCO, fugacity, siderite t 2 Dan * Qtz + 02 = 4 Fay * 3 Phe + S, would gradually replacethe magnetitefield (and part 5 Dan * 7 Or= 8Ut + 9 Phe + 9 Qtz + 3 52 of the pyrrhotite field). The lines of equal danalite content in helvite solid solutionswould be deflected 4. 2 Dan * 8 S, = 3 Py + 3 Phe + 6 Qtz + 4 Oz upwards as they enteredthe siderite field (to a slope ( 2 Dan * 4 Sr= 8 Po + 3 Phe + 6 qtz + 4 Oz of +1, instead of +7/3 as in the magnetite field). Eventually, increasingCO' fugacitieswould lead to the destruction of danalite, by reactionssuch as the * Abbreviatlons are es ln Table 1. following: 358 BURT: STABILITY OF DANALITE

Table 3. Selectedassociations ofdanalite

Locallty Association References

Cape Ann, Massachusetts CavlEl-es ln granlte. Cooke, 1866 Danalite altered to slderlte, phenakite, Palaehe,1907 qttartz, pyrite, sphalerite. Pough,1936

Iron Mountaln, Bartlett Metasomatlcally replaced granlte. Wadsworth,1880 New Hampshlre Danallte-helvlte solLd solutLons overgrowing Glass et aL., 7944 phenakite, wlth nagnetite, pyrite, Warner et a1., 1959 sphalerlte, quartz, galena, , Barton and Goldsmith hematlfe, and pyroxene. 1968 Dunn, 1976 Authorts vlslts, 1976, 1977

North End Peak, Iron Mountaln "Ribbon rock'r banded skarn replacing class et al., L944 New Mexlco limestone. Jahns and Glass, 1944 Danalite wlth fluorlte, magnetite, grossularite, chloriCe, and biotlte.

Needlepoint Mt., McDame area, Skarn ln llmestone. Thompson,1957 3.C., Canada Danallte wlth nagnetite, quartz, chlorlte, fluorite, and native blsmuth-

Redruth, Cornwall, England Purchased speclmen. Miers and Prlor, 1892 Danallte with quartz, arsenopyrlte, sphalerite, chalcopyrlte, and chlorite.

New Tolgus shaft, Redruth, A11 are skarn-related veins 1n greenstone. Ktngsbury, J.961 Cornwall, England Danallte wlth chlorlte, arsenopyrlte, pyrlte, l,evant Mlne, St. Just, chalcopyrlte, and sphalerlte; at Cornwall, England lndivlduaL localltles wlth calcite. Tretoll Mine, Lanlvet, fluorlte, and . Cornwall, England Wheal Maudlln, Lanlivery Cornwall, England

Mlhara Mlne, Hlroshima Danallte wlth phenaklte ln nonzonite near Aoki and Hida, 1974 Prefecture, Japan skarn contac!. Phenakite in adjacent f eldspar-f luorlte-blotlte-scheellte skarn.

Unspeclfled, U.S.S.R. . Orlov et a1., 1961 Danalite replaces beryl; ls ln turn replaced Cerny,1970 by bertrandlte, phenaklte, pyrite, and hematite.

Precmbrlan Russlan Quartz velns ln altered granlte and diabase. zubkov et aI., L972 platform, U.S.S.R. Danallte (51 at. % Fe) altered by hematite. Helvlte, phenaklte, nuscovj.te, calcite, magnetlte, acnite, and other minerals occur in related rocks.

Far East, U.S.S.R. Complex tLn-rare netal deposlts. Marshukova and Danallte ln plagioclase-cllnopyroxene skarns Pavlovskll, 1969 ln marble with casslterlte, scheelite, garnet, fluorlte, and arsenopyrlte. Also, danalite 1n dlopslde-magnetite skarns with chrysoberyl, phlogoplte, idocrase, epidote, garnet, hastlngsite, fluorlte, , and chalcopyrice.

Discussion the danalite field. (On Figure 2, reactions2 and 5 of Table2 also have slopesof +1.) If sulfatespecies are In reducing, ore-depositingfluids, HrS is a much ignored, the stability of danalite on Figures 2 and 3 more abundant speciesthan either S, or O, (Holland, could thereforebe summarizedby stating that at low 1965).On Figures 2 and 3, in the presenceof water, HrS fugacities,danalite oxidizesto a mixture of mag- lines of equal HrS fugacity would have a slopeof *1, netite, phenakite, and quartz (or fayalite). At high more-or-lessparallel to the direction of elongationof HrS fugacities, it sulfldizes to a mixture of pyrrhotite B(IRT: STABILITY OF DANALITE 359

(or pyrite), phenakite, and quartz. Danalite solid so- the Zn and Mn ends of the helvite seriesnoted by lutions are stable over a narrow intermediate range Dunn (1976). of HrS fugacities that pinches out with increasing fugacities of S, and O, (or SO'). Acknowledgments At low temperatures, in hydrous systems, ber- The Interlibrary Loan Service, Arizona State University Li- trandite, BeoSi'O'(OH)r, presumably replaces phena- brary, is thanked for assistance in locating several Russian refer- kite in the above equilibria (Burt, 1978). If CO, is enoes, as is Arthur Barabas for assistance with transportation to Iron Mountain deposit, New Hampshire. P. R. Buseck, S. B. added to the system, siderite can replace the iron the Romberger, and P. J. Dunn provided useful reviews. I am also oxides, as mentioned. grateful to Tom Young, Jenelle Lorello, and Mike Smith for com- Numerous examples of these equilibria are given puting assistance and specimen preparation, as well as to Terry in Table 3. This table only includes danalite occur- Sprowl for typing the manuscript and to Sue Selkirk for drafting ren@s for which fairly complete mineral associations the figures. Partial support for this research was obtained from the Faculty Grant-In-Aid Program, Arizona State University. have been described; for other occurrences consult, e.g., Glass et al. (1944); Beus (1966); Gorman (1975); and Dunn (1976). References One of the more interesting associations of miner- Aoki, Y. and N. Hida (1974) Geology and genesis of beryllium ore als in Table 3 occurs in the Fe-Be deposits at Iron deposit, Mihara mine, Hiroshima Prefecture, Japan [in Japa- Mountain, Bartlett, New Hampshire. Here danalite- nesel. Kozan Chishitsu (Mining Geol', Japan), 24' 20l-2ll (not Chem. Abstrdcts,8l, #155889, 1974)' helvite solid solutions, in places growing on phena- seen; extracted fron Barton, W R. and C. E. Goldsmith (1968) New England beryl- with magnetite, quartz, py- kite, are also associated lium investigations. Lr. S. Bur. Mines, Rept. Inv. 7070- rite, sphalerite, galena, and fluorite (Barton and Beus, A. A. (1966) Geochemistry of beryllium and genetic types of Goldsmith, 1968). The danalite crystals are zoned, beryttium deposits [in transl.]. Freeman, San Francisco. with helvite cores and danalite rims (with up to 86 Burt, D. M. (1974) Concepts of acidity and basicity in petrology- approach. Geol. Soc. Am. Abstrocts reith mole percent Fe end member, according to Dunn, the exchange operator Programs, 6, 67+676. local hydro- 1977). The deposit appears to be a - (19'11) Chalcophile-lithophile tendencies in the helvite thermal replacement of the Conway granite. group: genthelvite stability in the system ZnO-BeO-Al2O3- At some deposits not listed in Table 3, danalite- SiO2-SO-r-F2O-q (abstr.). Am. Geophys. Union Trans., 58, equivalent assemblages occur alone. For example, 1242. - (1978) Multisystems analysis of beryllium mineral stabil- Hiigi and Rowe (1970) summarize numerous hema- ities: the system BeO-AI2O3-SiO2-H2O. Am. Mineral.' 63' 66+ a hematite- tite-phenakite-quartz occurrences and 676. bertrandite-quartz occurrence in the Alps. Nearly Cernf, P. (1970) Review ofsome secondary hypogene parageneses Fe-free helvite occurs with hematite and quartz at an after early minerals. Freiberger Forschungshefte, "unspecified locality in the USSR; bertrandite is also c270,4't-6'.7. V. (Ed.) (1972) Silicates with single and paired sili- present with hematite (Pavlova et al., 1966; Pavlova, Chukhrov, F. cate tetrahedra Russian]. Mineraly, Spravochnik, J, no. l. (cf. [in 1970). Numerous other examples could be ciled Nauka Press, Moscow. Pough, 1936; Egorov,1967; Chukhrov, 1972). Cooke, J. P., Jr. (1866) On danalite, a new mineral species from As the above assemblageswith hematite imply, the the granite of Rockport, Mass. lrn. J' Sci., 42,73-79- group. unique feature of danalite, as compared with Zn and Dunn, P. J. (t976) Genthelvite and the helvine Mineral. Mag., 40, 62'l-636. Mn end members of the helvite group, is its sensitiv- Egorov, I. N. (1967) Geological and mineralogical features of hy- gen- ity to oxidation. The reactions that determine drothermal beryllium mineralization related to a granitic massif thelvite and helvite stabilites in nature are apparently [in Russian]. Sov. Geol',10, 133-138. sensitive only to the chemical potential of the com- Finger, L. W. and D. M. Burt (1972) REAcrIor, a Fortran IY 'f chemical reactions. Carnegie Inst. ponent SO-, (or to the fugacity ratios o,and f ^,"/ computer program to balance ",/f Wash. Year Book, 71,616420. cf. reactions 2 and 5 of Table 2). This potential f ',o: Glass, J. J., R. H. Jahns and R. E. Stevens (19'{4) Helvite and dan- can be related to the chalcophile-lithophile tenden- alite from New Mexico and the helvite group. Am. Mineral., 29, cies of the elements (Burt, 1974). The chalcophile 163-19 l. tendencies of the helvite group elements can be ex- Gorman, R. C. (1975) Mineral Division Repott. Annual Rept- (not seen; ex- pressed as the inequalrty Zn >> Fe > Mn (Maraku- Govt. Chem. Lab., , 19'14,22-31 tracted from Mineral. Abstracts, 76, #3072' 19'16). shev and Bezmen, 1969). This concept explains the Holland, H. D. (1965) Some applications of thermochemical data tendency for genthelvite to occur in distinctly alka- to problems of ore deposits IL Mineral assemblages and the line, sulful-poor igneous environments (Burt, 1977), composition of ore-forming fluids. Econ. Geol., 60, I l0l-l 166. and also explains the otherwise puzzling gap between Htgi, T. and D. Rowe (1970) Beryllium Mineralien und Beryl- 360 BURT: STABILITY OF DANALITE

liumgehalte granitischer Gesteine der Alpen. Schweiz.Mineral. tion product of danalite from Gloucester, Mass. Am. J. Sci., 24, Petrogr. Milt., 50, 45480. 252-255. Jahns,R. H. and J. J. Glass(1944) Beryllium and tungstendepos_ Pavlova, I. G. (1970)On the evolution of the compositionof be- its of the lron Mountain district, Sierra and Socorro Counties, ryllium milerals at the metasomatic proc€ssesin greisens. In New Mexico. U. S. Geol. Sum.Bull.,945-C,45-79. Problems of hydrothermal ore deposition Internat. Uniqn Geol. Kingsbury, A. W. G. (1961)Beryllium minerals in Cornwall and Sci. Ser. A, no.2, p.334-348. SchweizerbargStuttgart. Devon: helvine, genth€lvite, and danalite. Mineral. Mag., 32, 921-940. paragenesis,and conditions of formation of helvite in greisens Marakushev, A. A. and N. L Bezmen(1969) Chemical affinity of [in Russian].Zap. Vses.Mineral. Obshch.95,674-689. metals for oxygen and sulfur. Geol. Rudnykh Mestorozhdeniy, Pough,F. H. (1936)Phenakit, seine Morphologie und Paragenesis. lI,8-23. [transl.Inl. Geol. Rev.,i,3, tT}t-l.tg4 (1974\1. NeuesJahrb. Mineral. Abh., Beil. Band,A7I,29l-341. Marshukova, pavlovskii N. K. and A. B. (1969) Danalites from Thompson, R. M. (1957) Danalite from British Columbia. Can. complex rare metal deposits [in Russian]. Trady Mineral. Mineral., 6, 68-71. Muz. im. A. E. Fersman,Akad. Nauk SSSX, ,19,lg9_191. Wadsworth, M. E. (1880) Danalite from the iron mine, Bartlert, Mel'nikov, O. K., B. M. Litvin and S. p. Fedosova(196g) produc_ N. H. Boslon Soc. Nat. History Proc., 20,28+286. tion of helvite-groupmmpounds [in Russian].In A. M. Loba- Warner, L. A., W. T. Holscr, V. R. Wilrnarth and E. M. Cameron chev, Ed., Gidrotermal'nyiSintez Kristalloa p. 167-l?4. Nauka (1959) Occurrenceof nonpegmatite beryllium in the United Press,Moscow. States.U.S. Geol. Sun. Prof. Pap. 318. Miers, H. A. and G. T. Prior (1892)Danalite from Cornwall. Mrz_ Zubkov, L. 8., N. L Galadzheva and A. B. Chernyakhovskiy eral. Mag., 10, lO-14. (1972)Acrcssory helvite minerals from quartz veins and mcta- Orlov, Yu. L., A. I. Ginzburg pinevich para_ and G. N. (1961) somatized rocks of the Precambrian Russian platform [in Rus- genetic interrelation of beryllium minerals in some pegmatite sianl. Mineral. Sb. (L'vov. Gos. Univ.),26,360-367. veins [in Russian]. Trudy Mineral. Muz. im. A. E. Fersman, Akad. Nauk SSSR,11, 103-113. Manuscriplreceived, August 18,1977; Palache,C. (1907)Mineralogical notes,2. phenaciteas an altcra_ acceptedforpublication, December 17, 1979.