Metahewettite, Ca(V5+6O16)(H2O)3, from Hodzha-Rushnai-Mazar, southern Kirgizia: occurrence and crystal structure

Abstract

Metahewettite was encountered in hypergene crusts in Paleozoic carbon-silica schists included in the carbon mélange matrix at Hodzha-Rushnai-Mazar in southern Kirgizia. Schist outcrops are marked by multicolored yellow, orange, brown and green crusts of vanadates and sulfates of chalсoalumite group, volborthite, V-bearing phosphates, Cr-V-bearing members of alunite subgroup, members of the pascoite group and vanadium-bronze oxides, including metahewettite. Metahewettite is acicular with individual crystals up to 1 mm in length, and forms radial aggregates 2-3 mm in diameter, or flattened aggregates in narrow fissures. Crystals are dark-brown to reddish-brown with a golden sheen. The crystal structure of metahewettite, Ca(V The chains and ribbons link by sharing polyhedron corners to form sheets of V polyhedra parallel to (001). These sheets are linked by interlayer Ca that occupies two interstitial Ca sites, and by (H 2 O) groups.