spherulite

thumb|Spherulites in volcanic ash|rhyolitic ash, Hailstone Trail, Echo Canyon, [[Chiricahua Mountains, Arizona]] thumb|Spherulite markings on snowflake obsidian thumb|thin section|Photomicrograph of [[rhyolite, showing spherulitic texture (brown, between grey to white crystals)]]

In petrology, spherulites () 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.