Structural generic features of pentaborates as the members of the OD family having various extents of condensation of fundamental building blocks

Crystal-chemical analysis is made for the pentaborate family on the basis o f the OD theory advanced by Dornberger-Schiff with nondimensional, unidimen sional, and two-dimensional building blocks being distinguished. Four types of topologically equivalent nondimensional blocks correspond to fundamenta l building blocks (FBBs) in Clark and Christ's classification system. Symme try groupoids are assigned to all of the structural groups considered. Stru nz's classification scheme is corrected. Three structural generic branches exist for pentaborates: (1) from ulexite through probertite (kaliborite) an d heidornite (tuzlaite) to type I hilgardites; (2) from ezcurrite (a) throu gh gowerite through nasinite with rho layer stacking to type I hilgardites or (b) through veatchites through biringuccite with tau layer stacking to t ype II hilgardites; and (3) from sborgite (santite) through ammonioborite t o larderellite and beta -RbB5O8.