Geoscience Ontology Description
Igneous rock in which the framework of the rock consists of crystals that are too small to determine mineralogy with the unaided eye; framework may include up to 50 percent glass. A significant percentage of the rock by volume may be phenocrysts. Includes rocks that are generally called volcanic rocks.
Need to make decision as to whether devitrified glass should be considered glass or microcrystalline framework for purposes of categorization