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Pandoraite-Ba and pandoraite-Ca, Ba(V (super 4+) (sub 5) V (super 5+) (sub 2) )O (sub 16) .H (sub 2) O and Ca(V (super 4+) (sub 5) V (super 5+) (sub 2) )O (sub 16) .H (sub 2) O, two new vanadium oxide bronze minerals in solid solution from the Pandora Mine, La Sal mining district, San Juan County, Colorado, USA

Anthony R. Kampf, John M. Hughes, Barbara P. Nash and Joe Marty
Pandoraite-Ba and pandoraite-Ca, Ba(V (super 4+) (sub 5) V (super 5+) (sub 2) )O (sub 16) .H (sub 2) O and Ca(V (super 4+) (sub 5) V (super 5+) (sub 2) )O (sub 16) .H (sub 2) O, two new vanadium oxide bronze minerals in solid solution from the Pandora Mine, La Sal mining district, San Juan County, Colorado, USA
The Canadian Mineralogist (March 2019) 57 (2): 255-265

Abstract

Pandoraite-Ba, BaV (super 4+) (sub 5) V (super 5+) (sub 2) O (sub 16) .3H (sub 2) O, and pandoraite-Ca, CaV (super 4+) (sub 5) V (super 5+) (sub 2) O (sub 16) .3H (sub 2) O, are two new vanadium-oxide-bronze minerals from the Pandora mine, La Sal district, San Juan County, Colorado, USA. Pandoraite-Ba and pandoraite-Ca are rare secondary minerals and occur on a matrix consisting of recrystallized quartz grains from the original sandstone. Crystals of carnotite are associated with pandoraite-Ba and crystals of finchite are associated with pandoraite-Ca. The minerals occur as thin, dark blue, square plates up to approximately 100 mu m across and approximately 2 mu m thick. Plates occur in subparallel to random intergrowths. The streak of both minerals is light greenish blue, and they display a vitreous, transparent luster and brittle tenacity; neither mineral displays fluorescence. The Mohs hardness of pandoraite-Ba and pandoraite-Ca is ca. 21/2. Cleavage for both minerals is perfect on {001}. For pandoraite-Ba, densitymeas = 3.24(1) g/cm (super 3) . For pandoraite-Ca, densitymeas = 2.91(1) g/cm (super 3) . Both minerals are biaxial (pseudo-uniaxial) (-). For pandoraite-Ba, alpha (epsilon ) =1.81(2), beta and gamma (omega ) = 1.84(1). For pandoraite-Ca, alpha (epsilon ) = 1.80(2), beta and gamma (omega ) = 1.83(1). Similar greenish-blue pleochroism is found in both minerals, Y and Z (O) > X (E). For pandoraite-Ba, the empirical formula from electron probe microanalysis (EPMA) (calculated on the basis of V + Fe + Al = 7 and O = 19 apfu) is (Ba (sub 0.83) Sr (sub 0.09) Ca (sub 0.05) Na (sub 0.03) K (sub 0.02) ) (sub Sigma 1.02) (V (super 4+) (sub 4.25) V (super 5+) (sub 2.38 ) Fe (super 3+) (sub 0.35) A (sub l0.02) ) (sub Sigma 7.00) O (sub 16) .3H (sub 2) O, and for pandoraite-Ca it is (Ca (sub 0.62) Ba (sub 0.07) Sr (sub 0.02) Na (sub 0.01) K (sub 0.01) ) (sub Sigma 0.73) (V (super 4+) (sub 3.70) V (super 5+) (sub 2.93) Fe (super 3+) (sub 0.37) A (sub l0.01) ) (sub Sigma 7.01) O (sub 16) .3H (sub 2) O. EPMA demonstrates that solid solution exists between the phases. Pandoraite-Ba is monoclinic (pseudo-tetragonal), P2, with a 6.1537(16), b 6.1534(18), c 21.356(7) Aa, beta 90.058(9) degrees , and V 808.7(4) Aa (super 3) , determined by single-crystal X-ray diffractometry. Pandoraite-Ca, inferred to be isostructural with the Ba-dominant phase, has a 6.119(8), b 6.105(8), c 21.460(9)Aa, beta 90.06(14) degrees , and V 801.7(15) Aa (super 3) , determined by refinement of powder diffraction data. The atomic arrangement of pandoraite-Ba was solved and refined to R1 = 0.0573 for 3652 independent reflections with I > 2sigma I. Pandoraite-Ba and pandoraite-Ca have vanadium oxide bronze layer structures formed of sheets of V (sub 7) O (sub 16) polyhedra that form the structural unit and (Ba,Ca)(H (sub 2) O) (sub 3) interlayers; the vanadium is of mixed valence (4 (super +) , 5 (super +) ), with the reduction of pentavalent vanadium occurring to balance the charge of the Ba "insertion" ions in partially occupied sites in the interlayer. A tetragonal synthetic analog is known.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 57
Serial Issue: 2
Title: Pandoraite-Ba and pandoraite-Ca, Ba(V (super 4+) (sub 5) V (super 5+) (sub 2) )O (sub 16) .H (sub 2) O and Ca(V (super 4+) (sub 5) V (super 5+) (sub 2) )O (sub 16) .H (sub 2) O, two new vanadium oxide bronze minerals in solid solution from the Pandora Mine, La Sal mining district, San Juan County, Colorado, USA
Affiliation: Natural History Museum of Los Angeles County, Department of Mineral Sciences, Los Angeles, CA, United States
Pages: 255-265
Published: 201903
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
Accession Number: 2019-029448
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
N37°37'60" - N37°57'00", W107°58'00" - W107°30'00"
Secondary Affiliation: University of Vermont, USA, United StatesUniversity of Utah, USA, United States
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201916
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