Nashite, Na3Ca2[(V4+V5+9)O28]*24H2O, a new mineral species from the Yellow Cat Mining District, Utah and the Slick Rock Mining District, Colorado: Crystal structure and descriptive mineralogy

Abstract

Nashite, Na3Ca2[(V4+V5+9)O28]•24H2O, is a new mineral species from the Little Eva mine, Yellow Cat District, Grand County, Utah, and the St. Jude mine, Slick Rock district, San Miguel County, Colorado, USA. Nashite occurs as blades on a corvusite-montroseite-bearing sandstone block intimately associated with calcite, gypsum, huemulite, pascoite, rossite, and sherwoodite. Nashite is bluish-green, with a light bluish-green streak. The mineral is transparent, with a subadamantine luster. Nashite does not fluoresce in short- or long-wave ultraviolet radiation, and has a hardness ca. 2. Nashite has a brittle tenacity, irregular fracture, and one good cleavage on {010}. Density (calc.) = 2.350 g/cm3 based on the empirical formula and single-crystal cell data, and density (calc.) = 2.343 g/cm3 based on the ideal formula and single-crystal cell data. Nashite is biaxial (–), with α 1.737(3), β 1.762(6), and γ 1.775(3). 2 V meas = 70(2)° and 2 V calc = 71°. Optic orientation is Y = b , X ≈ a . The mineral is pleochroic, with X greenish blue, Y yellowish green, and Z yellow, with X > Y >> Z . Electron probe microanalysis and the crystal structure solution gave the empirical formula (based on O = 52): (Na3.063K0.007)Σ3.070(Ca1.984Sr0.039)Σ2.019[(V4+V5+9)O28]•24(H1.995O). The simplified formula is Na3Ca2[(V4+V5+9)O28] •24H2O. Nashite is monoclinic, P 21/ n , with a 10.0099(3), b 21.8472(7), c 11.1504(7) A, and β 116.584(8)°. The strongest four lines in the diffraction pattern are [ d in A( I )( hkl )]: 9.044(100)(111, 101), 8.350(64)(110), 10.995(46)(020), and 2.9942(29)(331, 332, 303, 071, 310). The atomic arrangement of nashite was solved and refined to R1 = 0.0293. The structural unit in nashite is a partially-reduced decavanadate group, with a composition of [(V4+V5+9)O28]7–; charge balance in the structure is maintained by the [Na3Ca2(OH2)22•2H2O]7+ interstitial unit. The interstitial unit consists of chains of Na1 and Na2 octahedra and an irregular CaO2(OH2)6 polyhedron. The chains are linked to the structural unit by direct bonding to oxygen atoms of the [(V4+V5+9)O28]7– group and extensive hydrogen bonding between the H2O molecules of the interstitial group and the oxygen atoms of the structural unit. The mineral is named for Dr. Barbara P. Nash (b. 1944), Professor of Geology and Geophysics at the University of Utah.