metamorphic mineral

Kyanite (Blue or Blue-Grey)

Kyanite (Al2SiO5)

AI-generated identification · may be incorrect

Hardness: variable 4.5 to 7 on Mohs scale (anisotropic); Color: blue, blue-grey, green; Luster: Vitreous to pearly; Crystal structure: Triclinic (bladed/columnar); Cleavage: Perfect in one direction.

Hardness: variable 4
Color: blue, blue-grey, green
Luster: Vitreous to pearly

Identified March 14, 2026More metamorphic mineral →

Explore Kyanite (Blue or Blue-Grey) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: variable 4.5 to 7 on Mohs scale (anisotropic); Color: blue, blue-grey, green; Luster: Vitreous to pearly; Crystal structure: Triclinic (bladed/columnar); Cleavage: Perfect in one direction.

Formation & geological history

Formed at high pressure and relatively low temperatures during the regional metamorphism of clay-rich (pelitic) sedimentary rocks. Common in schists and gneisses.

Uses & applications

Used industrially for manufacturing heat-resistant ceramics (high-alumina refractories), spark plugs, and laboratory crucibles. High-quality specimens are used as gemstones and in collection.

Geological facts

Kyanite is unique because its hardness varies significantly depending on the direction of the crystal axis: it is about 4.5 to 5 parallel to the length of the crystal and 6.5 to 7 across it.

Field identification & locations

Identify by its characteristic bladed crystal habit and its unusual variable hardness. Commonly found in Brazil, Switzerland, and the USA (Appalachian Mountains). Look for flaky, elongated blue-tinted sticks in metamorphic outcrop.