mineral

Kyanite

Kyanite (Al2SiO5)

Hardness: 4.5-5.0 along axes, 6.5-7.0 across axes (anisotropic); Color: Blue, white, gray; Luster: Vitreous to pearly; Crystal structure: Triclinic; Cleavage: Perfect in one direction; Specific gravity: 3.53-3.67

Hardness: 4
Color: Blue, white, gray
Luster: Vitreous to pearly

Identified March 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed during high-pressure regional metamorphism of clay-rich sedimentary rocks (like shale or pelite). It is a metamorphic index mineral typically found in schists and gneisses.

Uses & applications

Used industrially in the manufacture of heat-resistant ceramics (mullite), spark plugs, and foundry molds. Fine specimens are used in jewelry as gemstones or for metaphysical collecting.

Geological facts

Kyanite is highly unusual because its hardness varies significantly depending on the direction it is scratched; it is the most well-known anisotropic mineral. It is a polymorph with andalusite and sillimanite.

Field identification & locations

Identify by its bladed crystal habit, distinct blue streak/color, and variable hardness. Commonly found in Brazil, USA (North Carolina), Switzerland, and Russia. Collectors look for deep indigo transparency.