Kyanite
Kyanite, or Cyanite, a mineral found chiefly in mica schist. Kyanite commonly occurs in long, three-sided crystals. It may be black, white, brown, blue, or green. Kyanite is used chiefly to make refractories (bricks and other articles able to withstand extremely high temperatures). The United States is the leading producer of kyanite.
Kyanite is a form of aluminum silicate, Al2SiO5.