Gneiss
“Banded beauty under pressure”
Metamorphic
Gneiss is a high-grade metamorphic rock recognized by its distinctive banded appearance — alternating layers of light and dark minerals. It forms under extreme heat and pressure deep within the crust, often from granite or sedimentary protoliths.
Composition
feldspar, quartz, mica, hornblende
Where Found
Acasta River (Canada), Greenland, Scandinavia, Appalachian Mountains (USA)
Mohs Hardness
6-7
Fun Fact
The Acasta Gneiss in Canada, at about 4.03 billion years old, is one of the oldest known rocks on Earth.
Test Your Knowledge
What process creates the distinctive alternating light and dark bands in gneiss?
Related Specimens
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