Crystal structure and crystal chemistry of melanovanadite, a natural vanadium bronze

• Published in: The American mineralogist Vol. 72; no. 5-6; pp. 637 - 644
• Main Authors: Konnert, Judith A, Evans, Jr
• Format: Journal Article
• Language: English
• Published: Washington, DC Mineralogical Society of America 01.06.1987
• Subjects: Cerro de Pasco Peru; Condensed matter: structure, mechanical and thermal properties; coordination; crystal chemistry; crystal structure; Exact sciences and technology; Inorganic compounds; melanovanadite; Minas Ragra; mineralogy; minerals; natural materials; nonsilicates; Pasco Peru; Peru; Physics; refinement; South America; space groups; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; thermal properties; vanadates; vanadium bronze; vanadium minerals; Water, oxides, hydroxides, peroxides; Cesium Vanadium Oxides Mixed; Molecular structure; Transition metal Compounds; Experimental study; X ray diffraction; Inorganic compound; Crystalline structure
• ISSN: 0003-004X; 1945-3027

The crystal structure of melanovanadite from Minas Ragra, Peru, has been determined in space group P1. The triclinic unit cell (non-standard) has a 6.360(2), b 18.090(9), c 6.276(2) A, alpha 110.18(4)o, beta 101.62(3)o, gamma 82.86(4)o. A subcell with b' = b/2 was found by crystal-structure analysis to contain CaV4O10.5H2O. The subcell has a layer structure in which the vanadate sheet consists of corner-shared tetrahedral VO4 and double square-pyramidal V2O8 groups, similar to that previously found in synthetic CsV2O5. Refinement of the full structure (R = 0.056) showed that the Ca atom, which half-occupies a general position in the subcell, is 90% ordered at one of these sites in the whole unit cell. Bond length-bond strength estimates indicate that the tetrahedra contain V5+, and the square pyramids, V4+.