MARTYITE, A NEW MINERAL SPECIES RELATED TO VOLBORTHITE: DESCRIPTION AND CRYSTAL STRUCTURE

Abstract

Martyite, Zn 3 (V 2 O 7 )(OH) 2 ·2H 2 O, a new mineral species from the Blue Cap mine, near La Sal, San Juan County, Utah, U.S.A., is named for its discoverer, Joe Marty, of Salt Lake City, Utah, who is also responsible for the discovery of three other new minerals from the same area. Martyite formed from post-mining leaching and oxidation of V–U oxide replacements of organic matter. It occurs as thin yellow-orange to red-orange plates and flakes with a rounded or irregular outline, up to 0.01 mm thick and 1 mm long, typically in irregularly intergrown mats and rosette-like clusters. The mineral has a pale yellow-orange streak, an adamantine luster, a Mohs hardness of about 3, and two cleavages, {001} perfect and {110} good. The measured density is 3.37(3) g/cm 3 , and the calculated density is 3.375 g/cm 3 . It is optically uniaxial (+), ω 1.797(3), e 1.806(3), and distinctly pleochroic: O >> E. Electron-microprobe analyses provided: ZnO 46.93, CoO 2.39, CaO 0.58, MgO 0.03, V 2 O 5 39.47, H 2 O 12.06 (calc.), total 101.46% which, based on V = 2 apfu and sufficient H for charge balance, yields (Zn 2.66 Co 0.15 Ca 0.05 )(V 2 O 7 )(OH) 1.72 ·2.23H 2 O. Martyite is hexagonal, P 3 m 1, a 6.0818(4), c 7.1793(10) A, V 229.97(4) A 3 , Z = 1. Its atomic structure [ R 1 = 1.84% for F o > 4σ( F o )] consists of edge-sharing sheets of Zn–O octahedra parallel to (001) linked in the c direction by divanadate (V 2 O 7 ) groups. The open space in the resulting framework is occupied by H 2 O molecules. The structure of martyite is topologically identical to that of volborthite, Cu 3 (V 2 O 7 )(OH) 2 ·2H 2 O. The Jahn–Teller distortion of one of the two non-equivalent Cu–O octahedra in volborthite results in a monoclinic symmetry. These minerals may have applications as molecular sieve materials.