Mineralogical Crystallography: IX. Borates

Boron belongs to the group of rare elements: its content in the continental crust is 0.0011 wt %. Despite this, the number of natural boron-containing compounds has now approached 300. Among them, 166 are borates. The pace of studying these compounds has been constantly increasing. The extraordinary geochemistry and mineralogy of boron is related to its inherent crystallochemical individuality, which manifests itself in a wide variety of borate complexes within borate-containing crystal structures. Among the latter, complexes of borate tetrahedra, complexes of triangles, and mixed complexes composed of interconnected tetrahedra and triangles stand out. The basic representatives of these three groups are discussed specifically in this sequence.