views updated

spherulite (adj. spherulitic) A spherical to ellipsoidal aggregate of radiating, fibrous crystals, usually quartz and alkali feldspar, found in glassy or felsitic, aphanitic groundmasses of igneous rocks. Spherulites range in diameter from less than 1 mm to about 1 m and are formed by the devitrification of quenched glassy igneous rocks which are usually silicic in composition.