Sillimanite

$Al_2OSiO_4$

  Family neosilicates
  Crystal system orthorhombic
  Color colorless, white, light yellow, blue, green or purple
  Streak color white
  Cleavage 1 perfect cleavage
  Hardness 6 to 7
  Density 3,2

Explanations: → Here List of minerals: → Here