Sturmanite, ideally Ca6Fe3+2(SO4)2.5[B(OH)4](OH)12•25H2O, is trigonal, P31c, Z = 2, with a 11.188(9), c 21.91(7) Å, V 2375.1(5) Å3. The crystal structure has been refined to an R index of 0.079. As in the case of ettringite, two coaxial elements parallel to  can be considered as the most distinctive features of sturmanite. The main one is a column of polyhedra formed by Fe-octahedra and Ca-polyhedra. The Fe(OH)6 octahedra are located along the three-fold axes that pass through the origin of the cell. They are linked to three VIIICa-polyhedra, located around the three-fold axes, in between the Fe(OH)6 octahedra. The second structural element parallel to  contains [SO4] and B(OH)4 tetrahedra; it is located along three-fold axes at (⅓, ⅔, z) and (⅔, ⅓, z). Both structural modules are linked to each other by a complex system of hydrogen bonds. On the basis of a complete determination of the structure, the chemical composition of sturmanite is close to Ca6[Fe3+0.6Al0.2Mn4+0.2]2[SO4]2.7[B(OH)3]0.3 [B(OH)4](OH)12•24H2O.
|Autori:||PUSHCHAROVSKY DY; LEBEDEVA YS; ZUBKOVA NV; PASERO M; BELLEZZA M; MERLINO S; CHUKANOV NV|
|Titolo:||The crystal structure of sturmanite|
|Anno del prodotto:||2004|
|Digital Object Identifier (DOI):||10.2113/gscanmin.42.3.723|
|Appare nelle tipologie:||1.1 Articolo in rivista|