What is Kyanite?
Kyanite is a blue aluminium silicate with striking bladed crystals and strongly directional hardness, making it a favourite of collectors and metamorphic-petrology students.
Mineralogy and crystal structure
Reference formula: Al2SiO5. Kyanite is one of the Al2SiO5 polymorphs, alongside andalusite and sillimanite. Its triclinic structure and pronounced anisotropic hardness are key identification features; a single Mohs value can be misleading if the test direction is not recorded. Kyanite is classified with silicates and has a triclinic crystal system. Typical hardness is 4.5–7 on the Mohs scale and specific gravity is approximately 3.5–3.7.
Colour, lustre and habit
Typical colours include blue, blue-green, white, grey. The usual bladed, prismatic, fibrous habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Kyanite forms in or is associated with medium- to high-pressure metamorphic rocks, especially pelites and aluminium-rich schists. Important documented localities include Nepal, Switzerland, Brazil, India, the United States, Kenya and Tanzania.
A blue blade with real geological character
Kyanite gives a collection both colour and a readable metamorphic story. Deep blue blades, pale fibrous aggregates and matrix-rich specimens each show a different side of the same pressure-temperature system, which makes this mineral useful for display as well as study.
Collecting and care
Protect thin blades and cleavage edges from impact; avoid using a hardness test on a valuable crystal.
