STRONTIOGINORITE: CRYSTAL-STRUCTURE ANALYSIS AND HYDROGEN BONDING

Strontioginorite, ideally SrCaB 14 O 20 (OH) 6 ·5H 2 O, from the Potash Corporation of Saskatchewan (New Brunswick Division) mine at Penobsquis, Kings County, New Brunswick, occurs in the Upper Halite member of the Windsor Group evaporites, and is associated with halite, sylvite, hilgardite, volkovskite and trembathite. Electron-microprobe analysis, supported by a single-crystal analysis of its structure, yield: CaO 7.47 (6.66–8.10), SrO 12.23 (11.30–13.69), (B 2 O 3 ) 61.22 and (H 2 O) 18.10, for a total of 99.02 wt.%. The empirical formula, based on 31 anions, is Ca 0.94 Sr 1.06 B 14 O 20 (OH) 6 ·5H 2 O. Strontioginorite is monoclinic, P 2 1 / a , with refined unit-cell parameters a 12.8171(4), b 14.4576(4), c 12.8008(4) A, β 101.327(1)°, V 2325.8(2) A 3 , Z = 4. The crystal structure refined to an R index of 0.024 for 6,784 unique, observed (>4σ F o ) reflections. The (010) sheets of borate polyhedra are weakly cross-linked by Sr and Ca polyhedra. The H 2 O and OH groups strengthen the cross-linkage with hydrogen bonding. The fundamental building block (FBB) within the structure, 8Δ6□:[ϕ] | | | −[ϕ] | | | −2Δ, is compared to that in the structure of other complex borates, such as nobleite and strontioborite.