ORTHOMINASRAGRITE, V4+O (SO4) (H2O)5, A NEW MINERAL SPECIES FROM TEMPLE MOUNTAIN, EMERY COUNTY, UTAH, U.S.A.

Abstract

Orthominasragrite, V 4+ O (SO 4 ) (H 2 O) 5 , is a new mineral species from Temple Mountain, Emery County, Utah. It occurs as rounded aggregates (up to ~200 μm across) of irregular grains that are pale blue to bright blue, depending on size. Orthominasragrite has a pale blue streak, a vitreous luster, and no observable fluorescence under ultraviolet light. It has no cleavage or parting. The Mohs hardness is ~1, and the calculated density is 2.00 g/cm 3 . Orthominasragrite is biaxial negative (pseudo-uniaxial) with α 1.529(2), β 1.534(2), γ 1.534(2), 2 V obs = 2(4)°, 2 V calc = 0°, non-pleochroic, X = b , Y = c, Z = a . Orthominasragrite is orthorhombic, space group Pmn 2 1 , a 7.246(4), b 9.333(6), c 6.210(4) A, V 420.0(3) A 3 , Z = 2. The strongest seven lines in the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are as follows: 4.699(10)(101,020), 3.322(5)(121), 2.865(4)(220), 2.602(3)(221,131,022), 3.734(2)(021), 3.622(2)(200), and 3.108(2)(002). Chemical analysis by electron microprobe gave VO 2 33.88, SO 3 31.97, H 2 O (calc.) 36.30, sum 102.15 wt.%; the proportion of H 2 O was determined by crystal-structure analysis. The resulting empirical formula on the basis of 10 anions (including 5 H 2 O) is V 1.014 S 0.991 O 5 (H 2 O) 5 ; the end-member formula is VO (SO 4 ) (H 2 O) 5 . Orthominasragrite is the orthorhombic form of (monoclinic) minasragrite. The crystal structure was solved by direct methods and refined to an R index of 4.4% for 1007 observed (| F o | > 5σ F ) reflections measured with an automated four-circle X-ray diffractometer using Mo K α X-radiation. There is one V site occupied by V 4+ and surrounded by one O atom and 5 (H 2 O) groups in an octahedral arrangement, with one short apical vanadyl bond (1.580 A), four similar equatorial bonds ( ), and one longer V–O bond (2.231 A) trans to the vanadyl bond. The structure consists of isolated (V 4+ ϕ 6 ) octahedra (ϕ: unspecified anion) and (SO 4 ) tetrahedra linked by hydrogen bonds.