Crystal structure of SrMn2[Si2O7](OH)2·H2O, a new mineral of the lawsonite type
Armbruster, Thomas; Oberhänsli, Roland; Bermanec, Vladimir
published: Feb 13, 1992
manuscript accepted: May 14, 1991
manuscript received: Jan 15, 1991
ArtNo. ESP147050401003, Price: 29.00 €
Abstract Crystals with the composition SrMn2[Si2O7](OH)2·H2O were found in a sugilite, serandite-pectolite rich sample from the Wessels Mine, Kalahari, South Africa. The crystal structure of the new compound with space group Cmcm, a = 6.255(1), b = 9.034(2), c = 13.397(2) A゚, Z = 4 was determined from X-ray single-crystal data (R = 0.048). The structure is of the lawsonite type where Al is completely replaced by Mn3+ and Ca by Sr. [Mn3+O6] octahedra forming edge-sharing chains parallel to a exhibit a Jahn-Teller distortion with four short and two long Mn3+-O distances. Sr is in eight-fold coordination and H2O is disordered on a split position. Together with orientite, macfallite, ruizite, and okhotskite the new compound belongs to a family of structures which have the fundamental building block [Mn3+2(OH)2(SiO4)2] and 6 x 9 A゚ cell dimensions in common.