Dumortierite from Madagascar, flat stone

The mineral dumortierite is an aluminum-boron-nesosilicaat having the chemical formula Al8BSi3O19OH. The purple-red to blue or green dumortierite has a hardness of 7 - 8.5 and stripe color is bluish-white to white. The mineral found in crystals or fibrous or fan-shaped aggregates, is translucent and has a silky sheen. The specific gravity of dumortierite is 3.3 - 3.4 to it has an orthorhombic crystal structure. The mineral is named after the French paleontologist Eugene Dumortier (1802-1873), who discovered the mineral. Dumortierite occurs in pegmatites and in pneumatolitische and metamorphic rocks and is quite rare. It is amongst others found in the former Soviet Union (Kazakhstan, Armenia, Yakutia), the US (New York, Arizona, Montana, California), Brazil (Minas Gerais), Germany (Black Forest), France, Scotland and Poland (Giant Mountains).