• journal_title：The Canadian Mineralogist
• Contributor：John M. Hughes ; Rebecca S. Derr ; Forrest Cureton ; Charles F. Campana ; Gregory Druschel
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.5.1267
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：5
• firstpage：1267
• section：Articles

Cavansite, Ca(VO)(Si₄O₁₀)•4H₂O, is a novel layer silicate, dimorphous with pentagonite. The earlier determination of its structure did not yield the location of the hydrogen atoms or clear resolution of the oxygen atoms of the H₂O molecules. In this study, structures are reported from data collected at 100(2) and 296(2) K, and they clearly resolve and allow refinement of the position of the H atoms. The 100 K and 296 K structures were refined to m>Rm>1 values of 0.0141 and 0.0389, respectively. Cavansite is orthorhombic with space-group symmetry m>Pcmnm>, with m>am> 9.7518(4), m>bm> 13.6854(6), and m>cm> 9.5965(4) Å at 100 K, and m>am> 9.7614(7), m>bm> 13.6666(10), and m>cm> 9.6049(7) Å at 296 K. Cavansite consists of two layers, a layer of silicate tetrahedra and a layer formed of irregular CaO₄(OH₂)₄ polyhedra and VO₅ square-based pyramids that alternate in ribbons parallel to [100] in (010); the layers join laterally at the four corners of the base of the V pyramid. The silicate layer consists of four- and eight-membered rings of silicate tetrahedra with apices pointing along [010] or [01̄0]. The four oxygen atoms in the Ca polyhedron that are not linked to the V square-based pyramids are part of H₂O molecules. Adjacent ribbons in (010) are linked by hydrogen bonding.