1. A spherical body or coarsely crystalline aggregate having a radial internal structure arranged around one or more centers.
2. A small, usually spheroidal body consisting of radiating crystals, found in obsidian and other glassy lava rocks.
3. In petrology (science of stones), small, rounded bodies that commonly occur in vitreous igneous rocks.

They are often visible in specimens of obsidian, pitchstone, and rhyolite as globules about the size of millet seed or rice grain, with a duller luster than the surrounding glassy base of the rock.