Mylonites

Part of speech: noun

Definitions

1. Rocks formed by intense mechanical deformation within fault zones, characterized by fine-grained, foliated textures due to ductile shearing; typically found in deep crustal levels where rocks undergo significant strain without fracturing
2. Metamorphic rocks created through extreme strain and recrystallization along fault surfaces, exhibiting a distinctive foliated and fine-grained structure that records ductile deformation processes deep beneath the Earth's surface
3. Geological formations resulting from the recrystallization and intense shearing of rocks along zones of crustal displacement, distinguished by their fine-grained, foliated appearance and evidence of ductile strain under high pressure and temperature conditions

Etymology: "Mylonites" is the plural of "mylonite," a noun for fine-grained rocks formed when fault movement grinds down the rock on either side of a fracture zone. The name comes from Ancient Greek "mulōn," meaning "mill," the same root behind words like "mill" and "molar" in English, with the suffix "-ite," used in mineral and rock names. The mill image fits the process closely: the rock is ground into a fine powder and then recemented, like flour pressed into something solid. The "-ite" ending, derived from Greek "-itēs," is the standard suffix geologists attach to names of rocks and minerals, so the word is a straightforward technical coinage rather than a term with a long popular history.