A type of metamorphic rock that contains sillimanite and other minerals, formed when clay-rich rocks are exposed to intense heat and pressure deep underground.
From fibro- (Latin fibra, 'fiber') + -lite (Greek lithos, 'stone'). The term emerged in geology in the 19th century to describe rocks with a fibrous mineral composition.
Fibrolite rocks record some of Earth's most extreme geological events—they form only in the deep roots of mountain ranges, making them time capsules of ancient continental collisions billions of years old.
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