Pentaborate polyanion in the crystal structure of ulexite, NaCaB 5O6(OH)6·5H2O

Abstract

Triclinic ulexite crystals contain isolated borate polyanions [B 5O6(OH)6]3- related to the well known pentaborate polyanion [B5O6(OH)4] - by addition of two hydroxyl groups to two opposite B-O triangles. The isolated ulexite polyanions form the [B5O7(OH) 4]n3n- chains previously found in crystals of the related mineral probertite, NaCa-B5O7(OH) 4·3H2O.