Vitrophyre

(from Latin vitrum, glass, and Greek porphyra, purple, crimson, dark-red), a general name for effusive rock consisting almost entirely of volcanic glass with a small quantity of mineral phenocrysts. Usually this is quartz or orthoclase porphyry with a glassy or cryptocrystalline base. The term “vitrophyre” is also used to refer to the structure of certain glassy rocks (so-called vitrophyric structure) containing a certain quantity of phenocrysts or microlites (for example, vitrophyric basalt, or vitrobasalt, and vitroandesite).