Kyanite

Kyanite Rock Professor Image

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 name, KYANITE, is from the Greek "kyanos" meaning blue. It is an aluminum silicate and is a metamorphic mineral. Kyanite is a polymorph with two other minerals: andalusite and sillimanite. (A polymorph is a mineral that shares the same chemistry with another mineral, but that has a different crystal structure).
 

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.

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