common form of tachylyte. Palagonite, an alteration product of basaltic glass. Hyaloclastite, a hydrated tuff-like breccia of sideromelane and palagonite. Pele's hair, threads or fibers of volcanic glass, usually basaltic. Pele's tears, tear-like drops of volcanic glass, usually basaltic. Limu o Pele (Pele's seaweed), thin sheets and flakes of brownish-green to near-clear volcanic glass, usually basaltic. Alteration Volcanic glass is chemically unstable and readily decomposes. Water molecules readily react with the open, disordered structure of volcanic glass, removing soluble cations from the glass and precipitating secondary (authigenic) minerals. As a result, lithification of volcanic ash is one of the fastest low-temperature lithification processes. Alteration of volcanic glass at mid-ocean ridges may have contributed significantly to the formation of massive sulfide deposits, and alteration of volcanic ash beds formed economically important zeolite and bentonite deposits. References Volcanology Glass in nature Volcanic rocks