Description
The mineral dumortierite is an aluminum-boron nesosilicate with the chemical formula Al8BSi3O19OH. Purple-red to blue or green dumortierite has a hardness of 7–8.5 and its streak color is bluish-white to white. The mineral, which occurs in crystals or fibrous or fan-shaped aggregates, is translucent and has a silky luster. The specific gravity of dumortierite is 3.3–3.4, and it has an orthorhombic crystal structure. The mineral is named after the French paleontologist Eugène Dumortier (1802–1873), who discovered it. Dumortierite occurs in pegmatites, pneumatolitic, and metamorphic rocks and is quite rare. It is found, among other places, in the former Soviet Union (Kazakhstan, Armenia, Yakutia), the United States (New York, Arizona, Montana, California), Brazil (Minas Gerais), Germany (Black Forest), France, Scotland, and Poland (Giant Mountains).
