Kyanite Schist
“Blue blades in a foliated matrix”
Kyanite schist is a metamorphic rock studded with elongated blue kyanite crystals set in a mica-rich matrix. Kyanite forms under high-pressure conditions during regional metamorphism, and its presence tells geologists that the rock was once buried to considerable depths in a mountain belt.
kyanite, quartz, muscovite, biotite, garnet, staurolite (occasional)
Appalachian Mountains (USA), Swiss Alps, Scottish Highlands, Minas Gerais (Brazil), Kenya, Nepal
4.5-7 (anisotropic)
Kyanite has the unusual property of having two different hardnesses depending on direction — it's 4.5 along its length but 6.5-7 across it, making it one of the most anisotropic common minerals.
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