Kyanite

Formula:  Al₂SiO₅

Origin of name:  From Greek for blue

Crystal system:  Triclinic

Crystal class:  -1

Twinning:  Common on {100}, lamellar

Unit cell: a = 7.11 Ǻ, b = 7.84 Ǻ, c = 5.57 Ǻ, α = 90.1°, β = 101.1°, γ = 106.0°

Colour:  Blue, colourless, white, gray, green, yellow, pink, nearly black

Diaphaneity: 

Luster:  Vitreous to pearly

Habit: 

Hardness:  4 to 7.5

Specific gravity:  3.53 to 3.67

Cleavage:  3; {100} perfect, {010} distinct, {001} parting

Tenacity:  Somewhat flexible

Streak:  Colourless

Synonyms/varieties:

Comments:  Trimorphous with andalusite and sillimanite