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🪨 Geology

Staurolite Mica Schist

Staurolite mica schist is a silvery mica schist studded with dark reddish-brown crystals of staurolite, an index mineral of medium-grade metamorphism. Staurolite often forms cross-shaped twins, and the name comes from the Greek for 'cross.'

3 min read • Updated October 2026 • Knowledge Wiki • AI-Assisted & Human-Supervised

Staurolite mica schist is a silvery mica schist studded with dark reddish-brown crystals of staurolite, an index mineral of medium-grade metamorphism. Staurolite often forms cross-shaped twins, and the name comes from the Greek for "cross."

Photograph of Staurolite Mica Schist (Barrovian Staurolite-Zone Pelitic Schist) — 📷 Photo: Shannon Heinle via Wikimedia Commons • CC0

🪨 Geology Guide Specimen: Open Staurolite Mica Schist in the CRV Science Rock & Mineral ID Guide to log the specimen, compare it with the other 6 subgroups of Metamorphic, and test your eye in LithoClade.

Fairy Crosses: How Do the Twins Form?

Staurolite crystals frequently grow as interpenetrating twins crossing at about 60 degrees or, in the cruciform type, at close to 90 degrees. These "fairy crosses" have been collected and worn as charms, and staurolite is the official state mineral of Georgia.

Index Mineral: What Does Staurolite Show?

In the Barrovian sequence, staurolite appears after garnet in mudstones, at roughly 520 to 650 degrees Celsius and moderate pressure. It is rich in iron and aluminum, forming where the host rock has enough of both. Its disappearance and the appearance of kyanite mark the next step in grade.

Texture: Why Does the Mica Matrix Matter?

The crystals are porphyroblasts, new crystals much larger than the matrix of mica and quartz that surrounds them. They grew in the solid rock and sometimes preserve older foliations as trails of inclusions, a record of the earlier history that the matrix has lost.