Pegmatite

Granite with giant crystals — centimeters to meters across — formed from water-rich final melts.

Pegmatite specimen — Photo: No machine-readable author provided. Zimbres assumed (based on copyright claims)., CC BY-SA 2.5, via Wikimedia Commons

How to identify pegmatite

Huge interlocking crystals of feldspar, quartz and mica.
May host tourmaline, beryl or garnet.
Often in veins cutting other rocks.

Often confused with

Granite
Granite has the same minerals but much smaller grains.
Compare side by side

Where it's found

Black Hills, South Dakota
Maine
Minas Gerais, Brazil
Madagascar

Uses

The world's main source of gem crystals, lithium, mica and feldspar.

Rock tumbling

Can be tumbled with care.

Did you know?

Some pegmatites contain single crystals over 10 meters long.

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