Perlitic Structure

Perlitic Structure, in Petrography, is a structure seen in some vitreous rocks. These rocks seem as if made up of little pearly or enamel-like spheroids, each of which is subdivided into a number of concentric coats by curved cracks, roughly parallel to its boundary. The spheroids usually lie packed between rectilinear or curved fissures that traverse the rock in all directions. Perlite is the name given to rocks showing this structure.