American Mineralogist, Volume 72, pages397-400, 1987 Blossite, a-Cu4+Y|+Or,a new fumarolic sublimate from Izalco volcano, El Salvador Paur,D. RonrxsoN Department of Geology, Southern Illinois University, Carbondale,Illinois 62901, U.S.A. JoHN M. Hucnps Department of Geology, Miami University, Oxford, Ohio 45056, U.S.A. MlnyANN L. Mal,rNcoNrco Department of Geology, Southern Illinois University, Carbondale,Illinois 62901, U.S.A. Ansrucr Blossite, a-CurYrOr, occurs as a fumarolic sublimate in the "Y" fumarole of Izalco volcano, El Salvador. The mineral is the natural analogue of the previously described synthetic phase, and is the the low-temperature polymorph of ziesite, 0-CurV'O', which was discoveredat the same site. The crystalsare orthorhombic, Fdd2, :u/rtha : 20.676(6), b:8.392(3), and c : 6.446(2)A. ttre crystal structurewas refined to R : 0.047. The atomic arrangementconsists of (100) planes of (VrOr)o- anionic groups; adjacent planes along [00] are linked by Cu2* in fivefold coordination. On the basis of previously deter- mined atomic arrangements,the a-B (blossite-ziesite)phase transition is of the non-near- est-neighborreconstructive type. Blossite occursas a equant, black anhedral crystalsup to 150 rrm in greatestdimension. The mineral has a metallic luster and a red-brown streak. The calculateddensity (Z: 8) is 4.05 I g/cm3. Blossite is opaque, and white in blue-filtered white light in air, with weak to moderate bireflectancein shadesof creamy-white, and a moderate anisotropy, from gray to creamy brown-gray. Minimum and maximum reflectancevalues (in air) are 481 nm, 14.6,15.3o/o;547 nm, 15.4,16.60/o;591 nm, 14.8,16.70/o, and,644 nm, 14.5,15.7o/o. The mineral is named in honor of Dr. F. Donald Bloss,past-President of the Mineralogical Society of America. INrnooucrroN Locll,rrv AND occuRRENcE Several high-temperature minerals have been discov- Izalco volcano, El Salvador,is a basalticcomposite cone ered in the summit crater fumaroles of Izalco volcano, El that has been intermittently active sinceits birth in 1770. Salvador, including shcherbinaite, bannermanite, stoi- The volcano risesto an altitude of 1965 m, with 650-m berite, fingerite, ziesite, and mcbirneyite. The latter four relief, and has an approximate volume of 2 km3. The minerals crystallize in the CuO-VrO, binary system and geology of the volcano is described by Meyer-Abich representthe natural analoguesofcompounds that were (1958),Rose and Stoiber(1969), and Stoiberet al. (1975). first discovered as synthetic compounds, although the As part of a long-term study of fumaroles at active naturally formed crystalshave provided the only material volcanoes, the fumarolic sublimate products of Izalco suitable for single-crystal X-ray studies for two of the volcano were collected by R. E. Stoiber and colleagues compounds.To thesefour coppervanadates is now added throughout the 1960s.Analyses of fumarolic gasconden- a fifth, a-CurVrOr, the low-temperature polymorph of satescollected simultaneouslydemonstrated that Cu and ziesite (B-CurVrOr).The authors are pleasedto name the V were distinctive elementsin the Izalco fumarolic gases. mineral blossitein honor of Dr. F. Donald Bloss,Virginia The first high-temperatureV mineral, shcherbinaite,was Polytechnic Institute and State University. Dr. Bloss has first discovered at Izalco (Stoiber and Durr, 1963), and servedthe mineralogical community in numerous capac- the existenceofseveral unidentified copper vanadatesin ities, including as President of the MSA. His researchin the fumarolic mineral suite was also noted (Stoiber and optical mineralogy is known to all mineralogists,and the Rose,1974). honor of a mineral in his name is certainly overdue. Spec- Blossite was collected from the "Y" fumarole (Stoiber imens of blossite have been deposited at the NMNH, et al., 1975) in the summit crater of Izalco volcano. The Smithsonian Institution. The mineral and mineral name mineral was found in the outer sulfate zone of the fu- have been approved by the IMA Commission on New marole, indicating a sublimation temperature between 100 Minerals and Mineral Names. and 200.C (Stoiber and Rose, 1974). Associated copper 0003404x/87l030H397$02.00 397 398 ROBINSONET AL.: BLOSSITE Vzos Mol % CuO Fig. |. Phasediagram of system CuO-VrOr (after Brisi and Molinari, 1958). vanadatesin the fumarole include stoiberite (CurVrO,o; Birnie and Hughes, 1979), ziesite (B-CurVrOr; Hughes and Birnie, 1980),fingerite [Cu,,Or(VOo)u;Hughes and Hadidiacos, 19851and mcbirneyite [Cur(YOo)r; Hughes et al., in prep.l. Only a few crystals of blossite have been isolated to date, generally 100-l 50 pm in greatestdimen- sron. Pnrvrous wonx Fig. 2. Arrangementof [VrOr]o-anionic groups in blossite. The copper vanadatesdiscovered allzalco volcano are Adjacent(100) planes of tetrahedraare linked by Cu atomsin all natural analoguesof compounds that crystallizein sys- fivefoldcoordination with oxygen.Cu atomsnot shown. tem CuO-VrO, (Fig. l), a binary system that was first studied by Brisi and Molinari (1958). Subsequentwork- ers have undertaken studies on both specificcompounds showed that of elements with Z > 10, only Cu and V within the CUO-VrO' system and phaserelations among were present. the various system compounds. Studies that are partic- Quantitative analyses were performed on an nrec ularly germaneto the presentwork are studieson ziesite, Autoscan microprobe operating at 20 kV. Cu and V metal the high-temperature polymorph of CurVrO, (Hughes and were used as standards, and the results grve 46.49(.07) Birnie, 1980; Mercurio-Lavaud and Frit, 1973a),as well wto/oCuO, 53.28(.27)wt0/o VrO, (the dewiationofanalyses as detailed structural studies on the synthetic analogueof frorn the mean in parentheses).Ideal CurVrOrhas 46.66 blossite presentedby Mercurio-Lavaud and Frit (1973b) wto/oCuO and 53.34 wto/oVrO'. and Calvo and Faggiani (1975). X-n lv cRYsrALLocRAPrrY Cnnvrrsrnv Blossite was first identified by comparison of its dif- A crystal of a blossite-fingeriteintergrowth was mount- fraction pattern to that of lcpps 26-566, the pattern of ed and polished for electron-microprobe microanalysis. synthetic a-CurVrOr. The pattern was obtained with a The crystal was estimated to be >800/oblossite from the I14.6-mm Gandolfi camera, Ni-filtered Cu radiation, in Gandolfi pattern. A qualitative energy-dispersiveanalysis vacuo. Sever"l extra lines were noted, but these were at- tributable to contamination of the crystals of blossite with either mcbirneyite or fingerite. Teeue1. Unit-cellparameters of blossiteand syn- A single-crystal precessionstudy of blossite was un- thetica-CurVrO, dertaken utilizing unfiltered Mo radiation. The available data on the synthetic analogueallowed rapid orientation of the crystal. Cone-axis and precessionphotographs of 20.676(6) 20.645(13) 20.68(1) D 8.392(3) 8.383(7) 8.411(5) the 0, l, and 2 levels along the a and b axes were taken 6.446(2) 6.442(12) 6.448(5) which displayed systematic extinctions consistent with Nole.' Columns are (1) This study; (2) Calvo and Faggiani spacegroup Fdd2 (43). (1975); (3) Mercurio-Lavaudand Frit (1973). One estimated The lattice parameters of blossite were refined from parentheses. standard deviationof least units cited is given in diffraction angles obtained from the Gandolfi photo- ROBINSON ET AL.: BLOSSITE 399 graphs and indices obtained from the precessionsuite as phase transition, three Cu-O bonds must be broken and well as Calvo and Faggiani (1975). The parameterswere reformed, although the final coordination polyhedra are in agreementwith those obtained by those authors. The identical. Thus, the phase transition is of the non-near- lattice parameterswere also refined using 22 diffraction est-neighbor reconstructive type; according to Buerger anglesmeasured on a four-circle diffractometer (Table 1). (1961), activation energiesare high for this type oftrans- formation, and reactions are tlpically sluggish.The fu- Cnvsrnr, srRUcruRE marole mineral suite from Izalco therefore contains zies- To further confirm that blossite is the natural analogue ite, which formed stably and persistsmetastably, and also of synthetic a-CurVrOr, a structure refinement of the nat- blossite, which formed when the fumarole temperatures ural phase was undertaken. However, the structure re- dropped below the inversion temperature of 710"C. finement was not completely successful.The only crystal large enough for data collection was an intergrowth of Prrvsrcll, PRoPERTIES blossite and fingerite, and thus not completely suitable. Blossite occursas equant, black anhedral crystalsup to Apparent overlap in intensities causedone oxygen atom 150 pm in greatestdimension. The mineral has a metallic to refine nonpositive defrnite when anisotropic tempera- luster. The crystals of blossite isolated to date are inter- ture factors were used. The structure ultimately refined grown with other fumarolic copper vanadatesor sulfates, to r : 0.047 vrith anisotropic temperature factors for all although severalcrystals are essentiallypure blossite. metal atoms and isotropic temperaturefactors for all oxy- Blossite has a red-brown streak, as determined from gen atoms. Our refinement servesto confirm the previ- the natural material and also noted by Mercurio-Lavaud ously determined structure. Becauseof the higher quality and Frit (1973b). The mineral does not fluorescein ul- of the previous determinations, however, the reader is traviolet radiation. The calculateddensity ofblossite (Z: referredto thoseworks for atomic coordinatesand aniso- 8; FW : 340.97)is 4.051 g,/cm3.Density valuesof 3.95 tropic temperature factors. A description of the structure (Mercurio-Lavaud and Frit, 1973b) and 3.969 g/cm3 is given below. (Calvo and Faggiani, 1975) have been reported for the Blossite is a member of that class of vanadates that synthetic analogue.No distinct cleavageswere observed crystallizes with V5+ in tetrahedral coordination with in blossite, although the anhedral, often-polycrystalline oxygen. The VOo tetrahedra in blossite dimerize in nature of the mineral grains prohibits good observations [VrOr]o groups, and thus the structure is closely related of cleavage. to that of the thortvetite-group compounds. The atomic Blossite is opaque to transmitted light.