Vanarsite

Vanarsite, NaCa 12 (As 3+ V 4+ 3.5 V 5+ 8.5 As 5+ 6 O 51 ) 2 ・78H 2 O, is a mineral that forms as very dark blue blades that are flattened on {100} and elongated on [010]. The crystals form in sub-parallel intergrowths in aggregates up to 5 mm long and are part of the cubic crystal system. The mineral is found in the Packrat mine in Colorado, USA in association with three mineral of similar composition, packratite, Ca 11 (As 3+ V 4+ 2 V 5+ 10 As 5+ 6 O 51 ) 2 ・83H 2 O, morrisonite, Ca 6 (As 3+ V 4+ 2 V 5+ 10 As 5+ 6 O 51 ) 2 ・78H 2 O, and gatewayite, Ca 11 (As 3+ V 4+ 3 V 5+ 9 As 5+ 6 O 51 )・31H 2 O. Vanarsite has been determined to be part of the vanadate, arsenite, and arsenate groups. Analytical methods were used to determine its chemical composition, physical properties, and structure.

Vanarsite, NaCa 12 (As 3+ V 4+ 3.5 V 5+ 8.5 As 5+ 6 O 51 ) 2 ・78H 2 O, is a mineral that forms as very dark blue blades that are flattened on {100} and elongated on [010]. The crystals form in sub-parallel intergrowths in aggregates up to 5 mm long and are part of the cubic crystal system. The mineral is found in the Packrat mine in Colorado, USA in association with three mineral of similar composition, packratite, Ca 11 (As 3+ V 4+ 2 V 5+ 10 As 5+ 6 O 51 ) 2 ・83H 2 O, morrisonite, Ca 6 (As 3+ V 4+ 2 V 5+ 10 As 5+ 6 O 51 ) 2 ・78H 2 O, and gatewayite, Ca 11 (As 3+ V 4+ 3 V 5+ 9 As 5+ 6 O 51 )・31H 2 O. Vanarsite has been determined to be part of the vanadate, arsenite, and arsenate groups. Analytical methods were used to determine its chemical composition, physical properties, and structure. ==Physical and Optical Properties== Vanarsite's physical properties show a very dark blue color, grayish blue streak, vitreous luster, and a hardness of 2 on the Mohs hardness scale. It also has transparent diaphaneity, brittle tenacity, curved fracture, and fair cleavage on {100}. Vanarsite has a calculated density of 2.460 g/cm 3 and a measured density of 2.48(2) g/cm 3 . Its optical class is biaxial (-) with an α value of 1.645(5), a β value of 1.677(calc), and a γ value of 1.681(calc). It has a 2V value of 37(2)° (measured), and its dispersion is not observed. It has orientation where X = b, Y ^ a = 12° in obtuse β and pleochroism where X = cornflower blue, Y = dark blue, Z = dark blue; X 4 (V), GaAs (As), Sr-titanate (Sr), albite (Na), and diopside (Ca). The constituents analyzed were normalized for a total of 100% weight combined with the calculated H 2 O. The weight percents for each cation in terms of oxygen are as follows: 0.63 for Na 2 O, 13.08 for CaO, 0.22 for SrO, 0.04 for FeO, 31.61 for As 2 O 5 , and 43.89 for V 2 O 5 . ==Crystallography and Structure== Powder and single crystal X-ray analysis were used in the determination of the crystallography and structure of the mineral. A Gandolfi-like motion was used in the powder diffraction method in the φ and ω axes to randomize the samples. The derived d-values and intensities were analyzed using JADE 2010 software. The structure of the mineral was determined with Rigaku CrystalClear software using an empirical multi-scan absorption. The structural unit was determined to be a heteropolyanion consisting of twelve distorted octahedra (V 4+,5+ O 6 ) around a central pyramid (As 3+ O 3 (arsenite)) and decorated by peripheral tetrahedra (As 5+ O 4 (arsenate)). Each peripheral tetrahedra shares three of its four vertices with octahedra (VO 6 ). The very dark blue color results from a V 4+ -V 5+ charge transfer in the V sites. ==References==

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