Boracite

Description

Boracite is a magnesium borate mineral defined by the chemical formula Mg3B7O13Cl. Mineralogically, it crystallizes in the orthorhombic-pyramidal system, though it frequently manifests in pseudo-isometric cubical or octahedral habits, which are attributed to a phase transition from an unstable high-temperature isometric form during cooling. These crystals often occur as dispersed grains or well-defined formations within anhydrite and gypsum deposits. Boracite possesses a Mohs hardness ranging from 7 to 7.5, a specific gravity between 2.9 and 3.0, and exhibits a conchoidal fracture without distinct cleavage. Optically, it displays a refractive index between 1.658 and 1.673. While insoluble in water, it remains soluble in hydrochloric acid. In ceramic applications, boracite serves as a significant boron ore and a practical source for boric acid; it is particularly utilized as a flux in glazes during mid-range firing processes, typically between 1000°C and 1200°C.