Volcanic glass is the amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas. Volcanic glass can refer to the interstitial, or matrix material in an aphanitic (fine grained) volcanic rock or can refer to any of several types of vitreous igneous rocks. Most commonly, it refers to obsidian, a rhyolitic glass with high silica content.
Other types of volcanic glass include:
- Pumice, which is considered a glass because it has no crystal structure.
- Apache tears, a kind of nodular obsidian.
- Tachylite (also spelled tachylyte), a basaltic glass with relatively low silica content.
- Sideromelane, a less common form tachylyte.
- Palagonite, a basaltic glass with relatively low silica content.
- 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.
Famous quotes containing the words volcanic and/or glass:
“Each of us, even the lowliest and most insignificant among us, was uprooted from his innermost existence by the almost constant volcanic upheavals visited upon our European soil and, as one of countless human beings, I can’t claim any special place for myself except that, as an Austrian, a Jew, writer, humanist and pacifist, I have always been precisely in those places where the effects of the thrusts were most violent.”
—Stefan Zweig (18811942)
“The glass has been falling all the afternoon”
—Adrienne Rich (b. 1929)