Pegmatite

Part of speech: noun

Pronunciation: /ˈpɛɡmətaɪt/

Definitions

1. A coarse-grained type of igneous rock, distinguished by its exceptionally large crystals and formation from slowly cooled magma
2. This geological rock variant features large crystal formations within a granitic base and typically originates from deep intrusive processes
3. A unique form of igneous rock characterized by its exceptionally coarse texture and the presence of very large mineral crystals formed from slow magma cooling

Etymology: Pegmatite takes its name from the Greek "pēgnumi," meaning "to fasten" or "to join," the same root that gave Greek "pēgma," a structure or framework. The idea behind the name is that the crystals in this rock seem to be fastened together, interlocking tightly as they grow, so the rock looks as though its minerals have been bound into one another. The "-ite" ending is the standard suffix that mineralogists and petrologists attach to rock and mineral names, so the word is essentially a descriptive technical coinage built from an ancient verb. The word was formed in modern scientific usage, not in classical antiquity, so the Greeks themselves never used it for rocks. It describes the coarse, intergrown texture of crystals that forms when a slowly cooling magma leaves large, well-developed grains within a granite-like mass.