Mylonite
“Crushed under pressure, beautifully streaked”
Metamorphic
Mylonite forms deep in fault zones where intense pressure and shearing deform rock without fully breaking it. The result is a fine-grained, streaky rock with distinctive flow patterns that record the direction of tectonic movement.
Composition
quartz, feldspar, mica, varies by parent rock
Where Found
Alpine Fault (New Zealand), Scottish Highlands, Appalachian Mountains, Scandinavian Caledonides
Mohs Hardness
6-7
Fun Fact
Mylonite gets its name from the Greek word 'mylon' meaning mill, because early geologists thought the rock had been ground up like grain in a mill.
Test Your Knowledge
How does mylonite deformation differ from the process that forms cataclasite?
Related Specimens
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