Fingerite, Curroz(Vot)Et a New Yanadium Sublimate from Lzalco Volcano, El Salvador: Descriptivemineralogy

Home , Euchlorine, Fingerite, Izalco (volcano), Ziesite

American Mineralogist, Volume 70, pages 193-j96, I9E5

Fingerite, CurrOz(VOt)et a new yanadium sublimate from lzalco volcano, El Salvador: descriptivemineralogy

JosN M. HucHes

Department of Geology Miami University, Oxford, Ohio 45056

aNo C. G. Haoruecos

Geophysical Laboratory 2801 Upton Street, N.W., Washington, D. C. 20008

Abstract

Fingerite, cu11o2(voa)6,o h€w copper vanadatemineral, has been discoveredin the summit crater fumaroles of Izalco volcano, El Salvador, Central America. The mineral, which occurs with thenardite and euchlorine, forms as a sublimate product from the volcanic gases.Fingerite occurs as euhedral, subhedraland anhedralcrystals up to 150pm in greatestdimension. Fingeriteis triclinic, PT,a :8.1576(6), b = 8.2691(5),c :8.0437(7)A, u: l}'t.t44(5), : F 91.389(7),y = 106.441(5)'and V = 493.84(0A3.ttre five most intense lines on the Gandolfipattern are 6.48(100;Tt0, 0tT;, 3.894(60;200,120),3.042(80; otz, t20),2.822(70; 122, 2-12)and 2.025(70 ; 203). Fingerite is black with a metallic luster and opaque.The calculateddensity of fingerite is 4-776gnlcc, z : l.In reflectedlight in air, fingeriteis mediumgray, non-pleochroicand exhibits 2 extinctions per complete rotation of the stage. The reflectance of randomly orientedgrains in blue-filteredwhite light in air is 2l-rTVo. Milligram amounts of the mineral exist. Type specimensare on deposit at the National Museum of Natural History, Smithsonian Institution and the Geophysical Laboratory, CarnegieInstitution of Washington.The mineral is namedin honor of Dr. Larry W. Finger, Geophysical Laboratory.

Introduction Locality and occurrence Naturally occurring Cu11O2(VOa)6has been discovered Izalco volcano is a basaltic composite cone that has in the fumaroles in the summit crater of Izalco volcano, been intermittently active since its birth in 1770. The El Salvador,Central America (13'49'N; 89'38'W). The volcano rises to an altitude of 1965m, with 650 m relief, authors are pleasedto name the new mineral fingerite in and has an approximate volume of 2 km3. The geology of honor of Dr. Larry W. Finger of the GeophysicalLabora- the volcano is describedby Meyer-Abich (195E),Rose tory, Carnegie Institution of Washington. Dr. Finger is and Stoiber (1969)and Stoiberet al. (197!. well known for his work in the fields of mineralogy, In 1963 the first-known, high-temperature vanadium crystal chemistry and crystal physics, and has served mineral was discoveredin the summit crater fumaroles of both the Mineralogical Society of America and the Inter- Izalco volcano. Since that time, the volcanic gasesand national Mineralogical Association through his service on sublimateminerals have been extensively studied. Sever- several committees. al new vanadium minerals have been discovered at the Type specimensoffingerite havebeen deposited at the site, including bannermanite [(Na,K)*Vl* Vl1*O,r; Geophysical Laboratory, Carnegie Institution of Wash- Hughesand Finger, l983al, shcherbinaite(VzOsi Hughes ington and the National Museum of Natural History, and Finger, 1983b),and three vanadatesin the system SmithsonianInstitution. The total amount of the new CuO-V2O5. Fingerite is the fourth sublimate mineral in mineral on hand is a few milligrams. The mineral and this chemicalsystem, joining stoiberite(Cu5V2O16; Birnie mineral name have been approved by the Commissionon and Hughes, 1979), ziesite (B-Cu2Y2O7;Hughes and New Minerals and Mineral Names, LM.A. Birnie, 1980),and Cu3V2O3(Christian and Hughes, in 0003-004x/85/0102-0193$02.00 193 r94 HUGHES AND HADIDIACOS: FINGERITE: DESCRIPTIVE MINERALOGY prep.). It has beendemonstrated that the mineralsformed Table l. Microprobe chemical analysesof fingerite as sublimatesfrom a vanadium-bearingvolcanic gas, at temperaturesup to 760"C and oxygen fugacities of 10-3'5 f* 2* 3 bar (Hughesand Stoiber, 1985). CUO s9.s3(33) 51.59 is found in the "Y" fumarole (Stoiber et al., Fingerite v^o- 39.65(40) 39.67(18) 38.4r 1975,Fig. l), one of five major fumaroles in the summit r00.00 crater of Izalco. The mineral occurs as black grains up to Total 150pm in greatestdimension. Fingerite was found in the outer sulfate zone of the fumarole, indicating a sublima- 1. f of 7 analyses of type crystal for chenical analyses' tion temperature between lfi) and 200"C (Stoiber and *, ot 15 aalyses of 3 cryslals. Fomula (o=25) | Rose, 1974). The mineral is intimately associatedwith Z. thenardite (NazSOr) and euchlorine [(Na,K)zCuro ctlo.oot.:(voc)6.2 (vo4) (SO4)r0(OH)7'l0HzOl; it is commonly intergrown with 3. Ideal cutto2 6. the latter. * One standard deviation in parentheses.

System CuGV2O5 The first study of compounds in the CUO-V2O5binary (1958),who systemwas undertakenby Brisi and Molinari comparisonof its diffraction pattern with that of CuaV2Oe identified five incongruently melting compoundsbetween (rcros 16-420;note that the most intense peak of rcros (Fig. The phases the CuO and VzOs end members l). 16-420is listed as 3.524, whereasthe original publication molar reported by Brisi and Molinari have CuO:V2O5 lists the peak as 3.594). The similar patterns suggested (stoiberite).Subse- ratiosof l:1,2:1, 3:1, 4:l and 5:1 that fingerite is the natural analog of Cu+VzOq.As shown both specific quent studies have been undertaken on subsequentlythe formula of fingerite is Cu11V6O26'Brisi phaserelations compoundswithin the binary system and and Molinari (1958), however, never analyzed the reac- Mercurio- among the various compounds. For example, tion products in their study of system CuG-VzOs. Their (1973) high tempera- Lavaud and Frit demonstratedthat a proposed chemical formulas were derived from the ratio phase (ziesite, ture polymorph of the 2:l ftCn2Y2Ol) of the system components at which the most intense the exists above 712"C.Fleury 0966, 1969)redetermined powder diffraction peaks of each product was observed. was able to repro- phaserelations within the system and This error in chemical formula perhaps explains the duce all of the compounds except CurVzOqreported by inability of Fleury 0966, 1969)to synthesizethe CuaV2Oe Brisi and Molinari. phaseof Brisi and Molinari. mineral by Fingerite was first identified as a new The formulation Cu11O2(VOa)6is preferred for fingerite to emphasizethe fact that it is a member of the class of vanadatesbased on tetrahedralVOa $roups, in contrast to the vanadium bronzes such as bannermanite,which have sheet structures based on linked, distorted VO6 octahe- dra. All the compoundsin Figure I are tetrahedral types: Cu(VOr)z (metavanadate,probably tetrahedral chains); Cuz(VzOz) (divanadate); Cur(VO+)z (orthovanadate); CurrOz(VOn)o (fi ngerite) ; and CusOz(VOa)2(stoiberite). ChemistrY Energy dispersive chemical analysesof fingerite were performed with a rpor seu/Microprobe. The analyses showed that among elements withZ > 9, only Cu and V are present. Quantitative wavelength dispersive analyses of fingerite were performed with rnol 35 and unc400 vzos electron microprobes. Cu metal and V metal were usedas Mol % CUO standards.The results of the analysesare summarizedin Fig. l. Phase diagram of the system CuO-V2O5 (after Brisi Table l. patterns fingerite and Molinari. 1958). Similar diffraction of Calculation of the empirical formula suggestedthat the the CuaV2Oe(4 CuO:VzOs) (Cu11V6O26,3.67CuO:V2O5) and CuaVzOg(CuO : VzOs : 4 : l) formula of Brisi and Molinari phase of Brisi and Molinari suggestthat their determination of (1958)was incorrect. On the basis of density, volume/ phasecomposition is in error. The high-temperaturepolymorph atom, and the empirical formula, a formula of of the 2CuO:V2O5 phase (FCrtz\zOz, ziesite) was not recog- oxygen (CuO:VzOs -- was proposedfor the nized in the Brisi and Molinari study. The phase 5CuO:V2O5 CuroVoOzs 3.33:1) (CusVzOro)= stoiberite. new mineral. A subsequentstructure determination, de- HUGHES AND HADIDIACOS: FINGERITE: DESCRIPTIVE MINERALOGY r95

scribedin the following paper (Finger, 1985),demonstrat- 8.0437Q)4, d = 107.144(5)', F = 91.389(7)","y : ed that the correct formula for fingerite is Cu11V6 106.441(5fand Y: 493.E46)43. O26[Cu11O2(VOa)5].Analysis 2 in Table I is thus in error Frecessionphotographs demonstratedthat fingerite is -3.8% by and +2.8Voof the amount present for CuO and triclinic, space group Pl or PT. The structure study by V2O5,respectively. Finger to be reported subsequently demonstrates that fingerite crystallizes in spacegroup PT. X-ray crystallography Diffraction patterns of fingerite in vacuo were obtained Physical properties with a 114.6 mm Gandolfi camera with Ni-filtered. Cu Fingerite occurs as euhedral, subhedral and anhedral radiation. Intensities were visually estimated. The in- crystals up to approximately 150 g,m in greatest dimen- dexed Gandolfi pattern, together with the pattern calcu- sion. The mineral is black with a metallic luster. The lated from the crystal structure, is presentedin Table 2. streak of fingerite is dark reddish brown, similar to the After definition of the reduced lattice by precession streak of hematite. methods, precession photographs were taken with Zr- Crystals of fingerite grow in both plateJike and equant filtered, Mo radiation. Cone-axis and precession photo- habits. Figure 2 is an SEM micrograph of a twin inter- graphs of the 0, I and2levels were taken along a, b, and growth of two plate-like twin members and one equant c. The axial parameterswere refined using 20values from twin member; the figure shows the relationship between the Gandolfi pattern, and these values were subsequently morphology and principal axesof the plate-like habit. The confirmed in the structure work by Finger to be reported two plate-like twin membersare related by a 180"rotation in the subsequentreport. Becauseofthe higher precision about [010]. ofFinger's data, those parametersare reported here. The No cleavageswere observed in optical or SEM exami- axial parameters were refined from the positions of 20 nation of fingerite crystals. independentobservations with 39. < Z0 < 54. measured The calculated density of fingerite (MW : 1420.65gml on a four-circle difractometer by the eight-reflection mol) is 4.776 gmlcc, Z = l. Sample scarcity prohibited centering method of King and Finger (1979).The refined direct measurementof the density. Crystals of fingerite unit cell parametersof the all-obtuse normal reoresenta- were observed to sink rapidly in methylene iodide (S.G. :8.1576(6), tion of the unit cell area U : g.Zei\S\, c : : 3.32 gm/cc). The density and volume/oxygen atom

Table 2. Calculated and observed powder patterns offingerite*

al(obs) d(calc) I(obs) I(calc) h k I q(006./ q(carc./ rtoos, r(cBfc, hkl

- 7,770 3.8 1o 0 - 2.r7\ '1.6 31,3 r 2 r - {.oJJ o o l 2.52' 2.540 !o ,i.3 zlt 7.53 7.528 10 2.' 010 2 q21 6\.2 r f r 5.48 6,\79 r00 13.? rro 6 lines, 6,\7\ 93.2 011 2.52-2.fi 5.80 5.795 10 rt.8 101 2.\t% \6.2 o Ja !.zsa \.735 50 55.r r I 0 2,\66 \T.r zd t 3,891+ 3.885 ou 20.5 200 z,t+j6 r7.7 2 2 L 3.882 1L.L fz o 2.\\7 39.r L2 3 3.517 3'639 ou !!.1 Eor 2.4].9 28.9 L22 3.512 23.r 111 2.358 25.7 2 2 0 3.r98 20.2 211 zo 10.6 o22 3,597 59.O 102 2,328 r3.2 321 3.293(d)3.309 OU 5r.3 201 r1.8 131 3,277 \7.5 10 2 c tAa c aA1 \o 6l+.3 f ri 3.192 3.187 10 r3,8 22r z.z I! 59.r 3 o z 3.108 3.115 t0 15.8 211 - 2.209 29.9 o!3 3.091 9.3 210 2.OTO 2.O5tt 50 8\.3 r!1 3.0\2 3,ol+\ 80 26.11 I 2 0 2.O25 2.O22 ?o 77,\ 203 3.ol{o 69.9 oL2 r.r+5 I .9Lr 30 12.r 5\o 3.020 \2.9 021 r.72O L.7r7 30 26.1 303 2.901 2.898 40 81.8 doz r.688 r.585 zo rl+.8 rL5 2.822 2.830 7O 2r.5 r22 - 1.588 33.r z T tr 2.820 ?8.r zTz 1 q?1 r (tt 20 L8.o E l+ I e,7i3 2.7\7 u0 6U,7 131 L.)25 !,)1) 20 19.r 2 l* 3 l.lLO Z. lro l+o 80.2 3 1 0 - r.tr89 52.9 5 0 1 2,7L6 38.5 z td. - 1.1+86 29.I 3 4 lr 2.668(d.)2.69\ [0 100.0 2 r 2 - r.40f 51.0 2oZ 2.680 63.0 oi: - r.\62 29,r rt l 2,666 !7.1 2tl - 1.1+10 35'7 L 2 l+ 2.5\3 29.2 031 1.358 7.357 lio 28.5 3 l+ 3 2.633 20.8 r30 1.343 1.313 20 5.\ \51

iobserred alata obtained froe 11!.6 m Gmdotfi c@ra, Ni-fiLtered. Cu radiatlon, veuu, vlswl lntelsity estiuates. Cslculated data obtained frcn the crystal structue . 196 HUGHES AND HADIDIACOS: FINGERITE: DESCRIPTIVE MINERALOGY

References Birnie, R. W. and Hughes,J. M. (1979)Stoiberite, Cu5V2O16, a new copper vanadatefrom Izalco volcano, El Salvador, Cen- tral America. American Mineralogist, 64, 941-944. Brisi, C. and Molinari, A. (1958)Il sistemaossido ramicoanidride vanadica. Annali di Chimica. Roma. 48, 263-269. Finger, Larry W. (1985)Fingerite, CurrOz(VO+)e,a new vanadium sublimatefrom Izalco volcano, El Salvador: Crystal structure. American Mineralogist, 70, 197-199. Fleury, P. (1966)Sur le systemeCuO-V2O5. Comptes Rendus de I'Academiedes Sciences,Paris, Ser. C,263,1375-13'17. Fleury, P. (1969)Etudes sur les systemesV2O5 ou Ag2O ou Tl2O3 et sur les combinaisons interoxydes correspondantes. Revuede Chimie Minerale,6, 819-81. Hughes,J. M. and Birnie, R. W. (1980)Ziesite, ftCtt2Y2Ol,a new copper vanadate and fumarole temperature indicator. American Mineralogist, 65, 1146-1149. (1983a)Bannermanite, a new Fig. 2. SEM photomicrographof a multiply-twinnedcrystal Hughes,J. M. and Finger, L. W. with pNa*V6O15. of fingerite,denoting b andc axesof thedominant twin member. sodium-potassiumvanadate isostructural Both the and pinacoidalforms are presenton the AmericanMineralogist, 68, 6f4-641. {100} {010} (1983b) chemistry dominanttwin member.Scale bar represents100 microns. Hughes,J. M. and Finger, L. W. The crystal of shcherbinaite,naturally occurring V2O5.American Mineral- ogist,68,1220-1222. (18.994) of fingerite are both within the range of other Hughes,J. M. and Stoiber,R. E. (1985)Vanadium sublimates in of copper vanadates. the fumaroles of Izalco volcano, El Salvador. Journal Research,in press. Fingerite is opaque in transmitted light. In reflected Volcanology and Geothermal King, H. E. and Finger, L. W. (1979)Ditrracted beam crystal light in air, fingerite is medium gray. The mineral is non- centeringand its application to high-pressurecrystallography' pleochroic grains and randomly oriented exhibit 2 extinc- Journal of Applied Crystallography, 12, 374-37 8. tions per complete rotation of the stage. Mandarino, J. A. (1976)The Gladstone-Dalerelationship part I. Determination of quantitative reflectance values was Derivation of new constants.Canadian Mineralogist, 14, 498- hampered by the small grain size of fingerite and the 502. extensiveplucking that resultedfrom polishing.Reflec- Mercurio-Lavaud, D. and Frit, M. B. (1973)Structure cristalline tance in blue-filtered white light in air was determinedby de la variete haute temperature du pyrovanadate de cuivre: comparisonwith standards.Randomly oriented grains of Cu2V2O7.Comptes Rendus de I'Academiedes Sciences,Par- fingerite were found to have a reflectance indistinguish- is, ser. C., 277, ll0l-1104. (1958)Active volcanoes of Guatemalaand El able from that of magnetite. Thus the reflectance of Meyer-Abich, H. Salvador. In Catalogueof the Active Volcanoes of the World fingeriteis estimatedatZlt2Vo. Including Solfataras, Part VI, Central America, p. 39-105. The mean index of refraction of fingerite, calculatedby International Association of Volcanology, Rome, Italy. the rule of Gladstoneand Dale with the specificrefractivi- Rose,W. I. and Stoiber,R. E. (1969)The 1966eruption of Izalco ty valuesgiven by Mandarino(1976), is 2.124. volcano, El Salvador. Journal of Geophysical Research, 74, Sample scarcity and size prohibited measurementsof 3119-3130. hardness.The mineral does not fluorescein short- or Stoiber, R. E. and Rose, W. L (1974)Fumarole incrustationsat long-wave ultraviolet radiation. active Central American volcanoes.Geochimica et Cosmochi- mica Acta. 38. 495-516. Acknowledgments Stoiber, R. E., Rose, W. L, Lange, I. M., and Birnie, R. W. (1975) of Izalco volcano (El Salvador) 1964-1974. This work wassupponed in part by grantPRM-8117456 from The cooling Jahrbuch,13, 193-205. theNSF (Hughes).Drs. JamesDavis and Thomas Laskowski of Geologische Owens-CorningFiberglas, Inc., arethanked for theirassistance in obtainingthe SEM photomicrographs.The manuscriptbene- fittedfrom reviewsby Drs. HowardT. Evans,Larry W. Finger, Manuscript received, February 7, 1984; RobertM. Hazen.Malcolm Ross and Hatten S. Yoder,Jr. accepted for publication, August 13, lgM.