a small radiating & usually concentrically arranged aggregation of one or more minerals generally of spherical or spheroidal shape formed by the radial growth of acicular crystals in a rigid glass about a common centre or inclusion

Subspherical aggregate of radial crystals in an otherwise glassy rock like obsidian. Created by devitrification of glass.

Spherulites, in petrology, are 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, and when they are examined with a lens they prove to have a radiate fibrous structure.

In polymer physics, spherulites are spherical semi-cristalline regions inside non-branched linear polymers.