Glassy Texture
Glassy Texture
the texture of volcanic rock that consists entirely of volcanic glass or that contains, in addition to volcanic glass, a small number of crystals (phenocrysts) in the groundmass. Glassy texture is most commonly found in rocks that are rich in silica and poor in calcium, magnesium, and iron. The rapid cooling of lava on the earth’s surface is conducive to the formation of this type of texture.