Dumortierite

Name:
Dumortierite
Detailed information:
A natural basic aluminum silicate, bright smalt-blue to greenish-blue in color, vitreous luster, d 3.26–3.36, Mohs hardness 7.

M Formula:	8Al2O3•6SiO2•B2O3•H2O (perhaps)
Occurrence:
U.S. (New York, Arizona, Nevada), France, Norway.
Use:
Spark-plug porcelain, special refractories.