mineral

Kyanite

Kyanite (Al2SiO5)

Hardness: variable 4.5–5.0 along crystals, 6.5–7.0 across. Color: typically pale blue to white/grey. Luster: vitreous to pearly. Crystal Structure: Triclinic. Cleavage: Perfect in one direction.

Hardness: variable 4
Color: typically pale blue to white/grey
Luster: vitreous to pearly

Identified March 16, 2026More mineral →

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Physical properties

Hardness: variable 4.5–5.0 along crystals, 6.5–7.0 across. Color: typically pale blue to white/grey. Luster: vitreous to pearly. Crystal Structure: Triclinic. Cleavage: Perfect in one direction.

Formation & geological history

Formed during high-pressure regional metamorphism of clay-rich sedimentary rocks (pelites). It is an indicator of deep crustal conditions, commonly found in metamorphic suites ranging from the Proterozoic to more recent orogenic belts.

Uses & applications

Used industrially in the manufacture of high-temperature refractory materials (spark plugs, kiln linings, mortars). Transparent gem-quality specimens are used in jewelry.

Geological facts

Kyanite is a polymorph with Andalusite and Sillimanite; they shared the same chemical formula but different structures based on pressure and temperature. It is unique for its extreme hardness anisotropy (different hardness depending on the direction it is scratched).

Field identification & locations

Identify by its bladed or elongated prismatic crystal habit and pale blue or grey color. It is commonly found in metamorphic terrains like the Appalachian Mountains (USA), Brazil, and the Swiss Alps.