kyanite An important metamorphic index mineral and one of the three Al₂SiO₅ mineral polymorphs, the other two being sillimanite and andalusite; sp. gr. 3.5–3.6; hardness 4–7 ; triclinic; light to darker blue, sometimes green or yellow, occasionally black; vitreous lustre; crystals usually long, columnar, often flattened and bladed, with occasional stellate intergrowths; cleavage pinacoidal, good {100}, {010}, parting {001}; occurs in regional metamorphic rocks that have been subjected to high pressures and low to moderate temperatures, and may be found in schists or gneisses associated with staurolite and garnet.

ky·a·nite / ˈkīəˌnīt/ (also cy·a·nite / ˈsīə-/ ) • n. a blue or green crystalline mineral consisting of aluminum silicate, used in heat-resistant ceramics.DERIVATIVES: ky·a·nit·ic / ˌkīəˈnitik/ adj.