Volcanic glass
Encyclopedia
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 rock
s. Most commonly, it refers to obsidian
, a rhyolitic glass with high silica content.
Other types of volcanic glass include:
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
. Like all types of glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
, 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
Matrix (geology)
The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...
material in an aphanitic (fine grained) volcanic rock or can refer to any of several types of vitreous igneous rock
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...
s. Most commonly, it refers to obsidian
Obsidian
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth...
, a rhyolitic glass with high silica content.
Other types of volcanic glass include:
- PumicePumicePumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
, which is considered a glass because it has no crystal structure. - Apache tearsApache tearsApache tears are rounded nodules of obsidian with diameter from about 0.5 to 5 cm. An Apache tear looks opaque by reflected light, but translucent when held up to light. Apache tears are usually black, but can range from black to red to brown...
, a kind of nodular obsidian. - Tachylite (also spelled tachylyte), a basaltBasaltBasalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic glass with relatively low silica content. - SideromelaneSideromelaneSideromelane is a vitreous basaltic volcanic glass, usually occurring in palagonite tuff, for which it is characteristic. It is a less common form of tachylite, with which it usually occurs together; however it lacks the iron oxide crystals dispersed in the glass, and therefore appearing...
, a less common form tachylyte. - PalagonitePalagonitePalagonite is an alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt. Palagonite can also result from the interaction between water and basalt melt...
, a basaltic glass with relatively low silica content. - HyaloclastiteHyaloclastiteHyaloclastite is a hydrated tuff-like breccia rich in black volcanic glass, formed during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It has the appearance of angular flat fragments sized between a millimeter to few centimeters...
, a hydrated tuff-like breccia of sideromelane and palagonite. - Pele's hairPele's hairPele's hair is a geological term for volcanic glass threads or fibers formed when small particles of molten material are thrown into the air and spun out by the wind into long hair-like strands. The diameter of the strands is less than 0.5 mm, and they can be as long as 2 meters. Pele’s...
, threads or fibers of volcanic glass, usually basaltic. - Pele's tearsPele's tearsPele’s tears is a geological term for small pieces of solidified lava drops formed when airborne particles of molten material fuse into tearlike drops of volcanic glass. Pele’s tears are jet black in color and are often found on one end of a strand of Pele's hair...
, tear-like drops of volcanic glass, usually basaltic. - Limu o PeleLimu o PeleLimu o Pele or Pele's seaweed is a geological term for thin sheets and subsequently shattered flakes of brownish-green to near-colourless volcanic glass lava spatter that commonly resemble seaweed in appearance, that have been erupted from a volcano...
(Pele's seaweed), thin sheets and flakes of brownish-green to near-clear volcanic glass, usually basaltic.