Chemistry: aluminum silicate, Al2SiO5 ♦ Crystal system: Triclinic ♦ Habit: columnar, forms columns ♦ Habit: Fibrous crystals ♦ Moh's hardness: 4 to 5 in one direction 6 to 7 in another direction ♦ Transparency: Transparent to translucent ♦ Luster: Vitreous to pearly ♦ Color: Blue principally, but also white, gray or green. Color is often not consistent throughout the crystal ♦ Cleavage: Good in one direction parallel to the flat blade face ♦ Fracture: Brittle ♦ Localities: Brazil, Virginia, North Carolina, Georgia, Switzerland, Russia, Serbia, India and Kenya.
The mineral forms blue fibrous blade-like crystals, often with a darker blue color near the center and a lighter color towards the outer edges of the blades.
Kyanite is a beautiful gemstone when faceted, but it is difficult to process as it has two different hardnesses depending upon direction. Parallel to the length of the crystal, kyanite has a hardness of 5. At right angles to this direction it is 7.