A nesosilicate mineral with composition Al₇(BO)₃(SiO₄)₃O₃. Dumortierite crystallizes in the orthorhombic system but well-formed crystals are rare; the mineral usually occurs in parallel or radiating fibrous aggregates. There is one direction of poor cleavage. The hardness is 7 on Mohs scale, and the specific gravity is 3.26–3.36. The mineral has a vitreous luster and a color that varies not only from one locality to another but in a single specimen. It may be pink, green, blue, or violet. Dumortierite is found in schists and gneisses and more rarely in pegmatites. In the United States it occurs at Dehesa, California, and at Rochester, Nevada, where it has been mined for the manufacture of high-grade porcelain.