The crystal structure of olshanskyite

X-ray intensity data for olshanskyite, Ca-2[B3O3(OH)(6)]OH . 3H(2)O, were c ollected from a crystal from the Fuka mine, Okayama Prefecture, Japan, usin g a PW1100 Philips single-crystal diffractometer. Olshanskyite is triclinic , a 7.953(4), b 9.873(9), c 7.362 (6) Angstrom, alpha 111.00(7), beta 94.65 (7), gamma 107.53(7)degrees, space group P (1) over bar, Z = 2. The crystal structure was solved and refined to R = 0.017 for 3833 observed reflection s and to R = 0.022 for all unique reflections (4419). The anionic group in the structure is a three-membered ring of boron-oxygen tetrahedra [B3O3(OH) (6)](3-). Two independent calcium atoms occur in a distorted square-antipri sm coordination with five oxygen atoms from the berate group and three hydr oxyl or H2O groups external to the berate cluster. The apparent discrepanci es between the unit-cell parameters and the formula unit of olshanskyite re sulting from the present research and those previously determined are attri buted to two alternative interpretations of the same chemical and X-ray pow der data. Analogies and differences between the crystal structure of olshan skyite and that of the analogous berate nifontovite Ca-3[B3O3(OH)(6)](2). 2 H(2)O also are discussed. Olshanskyite must be classified as a neso-tribora te, and its structure is based on finite berate clusters (FBB = 3 rectangle ).