Kyanite

A blue, bladed metamorphic mineral famous for having different hardness in different directions.

Kyanite specimen — Photo: User:Aelwyn, CC BY-SA 3.0, via Wikimedia Commons

How to identify kyanite

Long, flat, blue blades with streaky color.
A knife scratches it along the length but not across.
Splits along the blades.
Found in schist and gneiss.

Often confused with

Corundum
Sapphire is hardness 9 in every direction and forms barrels, not blades.
Compare side by side

Where it's found

Minas Gerais, Brazil
Nepal
North Carolina
Switzerland

Uses

High-temperature ceramics such as spark plugs and kiln linings.

Rock tumbling

Not suitable for tumbling.

Did you know?

Kyanite is about 4.5 hard along its length and about 6.5 across — one crystal, two hardnesses.

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