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Encyclopedia > Obsidian
Obsidian

Obsidian from Lake County, Oregon
General
Category Volcanic glass
Chemical formula 70–75% SiO2,
plus MgO, Fe3O4
Identification
Color Black, gray, dark green, red
Fracture Conchoidal
Mohs Scale hardness ~ 5 to 5.5
Luster Vitreous
Optical Properties Translucent
Specific gravity ~ 2.6
This article is about a type of volcanic glass. For other uses see obsidian (disambiguation).

Obsidian is a type of naturally-occurring glass formed as an extrusive igneous rock. It is produced when felsic lava erupts from a volcano cools rapidly through the glass transition temperature and freezes without sufficient time for crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid. Because of the lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as projectile points, and its modern use as surgical scalpel blades. Image File history File links This is a lossless scalable vector image. ... Image File history File links Download high resolution version (870x870, 89 KB) Summary A specimen of obsidian from Lake County, Oregon Licensing File links The following pages link to this file: Obsidian ... A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... For other uses, see Fracture (disambiguation). ... A conchoidal fracture is produced when some types of fine-grained mineral, such as obsidian and flint, are broken. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... Vitreous refers to a material in an amorphous, glassy state (in contrast to a crystalline state). ... In optics, transparency is the property of being transparent, or allowing light to pass. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Obsidian can refer to: Obsidian for the volcanic glass. ... This article is about the material. ... Extrusive refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks (etymology from latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminium, sodium, and potassium. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... In archaeology, a projectile point is an object that was hafted and used either as knife or projectile tip or both. ... For other uses, see Scalpel (disambiguation). ...

Contents

Origin and properties

A piece of rainbow obsidian.
A piece of rainbow obsidian.

Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline; in addition, its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% or more. Crystalline rocks with obsidian's composition include granite and rhyolite. Because obsidian is metastable at the earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. This breakdown of obsidian is accelerated by the presence of water. Obsidian has a low water content when fresh, typically less than 1 weight % water [1], but becomes progressively hydrated when exposed to groundwater, forming perlite. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Image File history File links Size of this preview: 725 × 600 pixelsFull resolution (2000 × 1655 pixel, file size: 1,011 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 725 × 600 pixelsFull resolution (2000 × 1655 pixel, file size: 1,011 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... For other uses, see Mineral (disambiguation). ... For other uses, see Crystal (disambiguation). ... A mineraloid is a mineral-like substance that does not demonstrate crystallinity. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ... Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminium, sodium, and potassium. ... R-phrases R42 R43 R49 S-phrases S22 S36 S37 S45 S53 Flash point non-flammable Supplementary data page Structure and properties n, εr, etc. ... For other uses, see granite (disambiguation). ... This page is about a volcanic rock. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... // The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... Expanded Perlite Perlite is an amorphous volcanic glass that has a relatively high water content. ... A tektite Tektites (from Greek tektos, molten) are natural glass objects, up to a few centimeters in size, which — according to most scientists — have been formed by the impact of large meteorites on Earths surface, although a few researchers favor an origin from the Moon as volcanic ejecta. ... This article is about Earths moon. ...


Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. Iron and magnesium typically give the obsidian a dark green to brown to black color. A very few samples are nearly clear. In some stones, the inclusion of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden (sheen obsidian) or rainbow sheen (rainbow obsidian). For other uses, see Iron (disambiguation). ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. ... Common in volcanic rocks, cristobalite is a high-temperature polymorph of quartz and tridymite. ...

Glass Mountain, a large obsidian flow at Medicine Lake Volcano.
Glass Mountain, a large obsidian flow at Medicine Lake Volcano.
Counterclockwise from top: obsidian, pumice and rhyolite (light color)

Image File history File links Glass_Mountain. ... Image File history File links Glass_Mountain. ... Penis Pump juice. ... Image taken in September 2003 by Daniel Mayer. ... Image taken in September 2003 by Daniel Mayer. ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... This page is about a volcanic rock. ...

Occurrence

Obsidian can be found in many locations around the world which have experienced rhyolitic eruptions. Among other places, large obsidan flows are found within the calderas of Newberry Volcano and Medicine Lake Volcano in the Cascade Range of western North America, and at Inyo Craters east of the Sierra Nevada in California. Yellowstone National Park has a mountainside containing much obsidian located between Mammoth Hot Springs and the Norris Geyser Basin, and deposits can be found in many other western U. S. states including Arizona, Colorado, Texas, Utah, and Idaho. Obsidian can also be found in the following countries: Armenia, Turkey, Italy, Mexico, Greece and Scotland. Map of Newberry Volcano and surroundings Newberry Volcano 7,985 ft (2,434 m) high is a large shield volcano located 40 miles (60 km) east of the Cascade Range and about 20 miles (30 km) southeast of Bend, Oregon. ... Penis Pump juice. ... “Cascades” redirects here. ... One of the Mono craters: an excellent example of a rhyolite dome. ... Official language(s) English Capital Sacramento Largest city Los Angeles Largest metro area Greater Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... “Yellowstone” redirects here. ... The geothermal areas of Yellowstone include several geyser basins in Yellowstone National Park as well as other geothermal features such as hot springs (including mud pots) and fumaroles. ... The geothermal areas of Yellowstone include several geyser basins in Yellowstone National Park as well as other geothermal features such as hot springs (including mud pots) and fumaroles. ... Official language(s) English Spoken language(s) English 74. ... Official language(s) English Capital Denver Largest city Denver Largest metro area Denver-Aurora Metro Area Area  Ranked 8th  - Total 104,185 sq mi (269,837 km²)  - Width 280 miles (451 km)  - Length 380 miles (612 km)  - % water 0. ... Official language(s) No official language See languages of Texas Capital Austin Largest city Houston Largest metro area Dallas–Fort Worth–Arlington Area  Ranked 2nd  - Total 261,797 sq mi (678,051 km²)  - Width 773 miles (1,244 km)  - Length 790 miles (1,270 km)  - % water 2. ... This article is about the U.S. state. ... Official language(s) English [1] Capital Boise Largest city Boise Largest metro area Boise metropolitan area Area  Ranked 14th  - Total 83,642 sq mi (216,632 km²)  - Width 305 miles (491 km)  - Length 479 miles (771 km)  - % water 0. ... This article is about the country. ...


Historical use

Obsidian arrowhead.
Obsidian arrowhead.

Obsidian was highly valued in certain Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads. Like all glass and some other types of naturally occurring rocks, obsidian breaks with a characteristic conchoidal fracture. It was also polished to create early mirrors. Image File history File links Obsidian arrowhead. ... Image File history File links Obsidian arrowhead. ... American Indian arrowheads of several shapes and functions Japanese arrowheads of several shapes and functions Arrowhead can refer to: the point of an arrow; some plants in the genus Sagittaria; the Arrowhead region of northeastern Minnesota; a place name in southern California, derived from an arrowhead-shaped geologic formation in... Stone Age fishing hook. ... This article is about the sedimentary rock. ... Conchoidal fracture describes the way that brittle materials break when they do not follow any natural planes of separation. ... A mirror, reflecting a vase. ...


Pre-Columbian Mesoamericans' use of obsidian was extensive and sophisticated, including carved and worked obsidian for tools and decorative objects. Mesoamericans also made a type of sword with obsidian blades mounted in a wooden body. Called a macuahuitl, the weapon was capable of inflicting terrible injuries, combining the sharp cutting edge of an obsidian blade with the ragged cut of a serrated weapon. The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on the Americas continent. ... This article is about the culture area. ... Obsidian was an important part of the material culture of Pre-Columbian Mesoamerica. ... A modern hammer is directly descended from ancient hand tools A tool or device is a piece of equipment which typically provides a mechanical advantage in accomplishing a physical task, or provides an ability that is not naturally available to the user of a tool. ... Swiss longsword, 15th or 16th century Look up Sword in Wiktionary, the free dictionary. ... Drawing of a 15th century macahuitl The maquahuitl, an Aztec obsidian-edged sword-club, was a devastating cutting weapon capable of easily cleaving to bone (according to a Spanish account, it was capable of easily decapitating a horse), but lacked a point (and thus couldnt be used for thrusting...


Native American people traded obsidian throughout North America. Each volcano and in some cases each volcanic eruption produces a distinguishable type of obsidian, making it possible for archaeologists to trace the origins of a particular artifact. Similar tracing techniques have allowed obsidian to be identified in Greece also as coming from either Melos, Nisyros or Yiali, islands in the Aegean Sea. Obsidian cores and blades were traded great distances inland from the coast. Milos (formerly Melos, and before the Athenian genocide Malos) is a volcanic island in the Aegean Sea. ... Nisyros (Greek: Νίσυρος; also transliterated Nissiros; see also List of traditional Greek place names) is a volcanic Greek island located in the Aegean Sea. ... Gyali (Greek Γυαλί glass, also spelled Yiali or Yali) is a volcanic Greek island in the Dodecanese, located halfway between the south coast of Kos (Kardamena) and Nisyros. ... Look up Aegean Sea in Wiktionary, the free dictionary. ...


Obsidian was also used on Rapa Nui (Easter island) for edged tools such as Mataia and the pupils of the eyes of their Moai (statues). Easter Island and its location Easter Island (Polynesian: Rapa Nui (Great Rapa), Spanish: Isla de Pascua) is an island in the south Pacific Ocean belonging to Chile. ... Ahu Tongariki, restored in the 1990s Moai are monolithic stone figures on Rapa Nui / Easter Island, Chile. ...


Modern archaeologists have developed a dating system Obsidian hydration dating to calculate the age of Obsidian artifacts. Archaeology or sometimes in American English archeology (from the Greek words αρχαίος = ancient and λόγος = word/speech) is the study of human cultures through the recovery, documentation and analysis of material remains, including architecture, artefacts, biofacts, human remains, and landscapes. ... Obsidian hydration dating is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian. ...


Current use

Pig carved in snowflake obsidian, 10 centimeters (4 in) long. The "snowflakes" are spherulites.

Obsidian is used in cardiac surgery, as well-crafted obsidian blades have a cutting edge many times sharper than high-quality steel surgical scalpels, with the edge of the blade being only about 3 nm wide [2]. Even the sharpest metal knife has a jagged, irregular blade when viewed under a strong enough microscope. When examined under an electron microscope an obsidian blade is still smooth and even. One study found that obsidian produced narrower scars, fewer inflammatory cells, and less granulation tissue in a group of rats.[3] Scan of a pig carved in snowflake obsidian. ... Scan of a pig carved in snowflake obsidian. ... Cardiac surgery is surgery on the heart, typically to treat complications of ischemic heart disease (e. ... For other uses, see Scalpel (disambiguation). ... Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. ...


Obsidian is also used for ornamental purposes and as a gemstone, for it possesses the peculiar property of presenting a different appearance according to the manner in which it is cut. When cut in one direction it is a beautiful jet black; when cut across another direction it is glistening gray. "Apache tears" are small rounded obsidian nuggets embedded within a grayish-white perlite matrix. For other uses, see Gemstone (disambiguation). ... Apache tears are a kind of nodular obsidian (volcanic black glass). ... Expanded Perlite Perlite is an amorphous volcanic glass that has a relatively high water content. ...


See also

Top stone is obsidian, below that is pumice and in lower right hand is rhyolite (light color) Obsidian is a type of naturally occurring glass, produced from volcanoes when the right kind of lava cools rapidly, e. ... Hyaloclastite is a hydrated tuff-like breccia rich on black volcanic glass, formed during volcanic eruptions under water or under ice. ... Tachylyte is a vitreous form of basaltic obsidian (volcanic glass). ... Basalt Basalt is an extrusive igneous rock, sometimes porphyritic, and is often both fine-grained and dense. ... Obsidian was an important part of the material culture of Pre-Columbian Mesoamerica. ... A flintknapper is an individual who shapes flint or other stone through the process of knapping or lithic reduction no shit sherlock, to manufacture stone tools, strikers for flintlock firearms, or to produce flat-faced stones for building or facing walls. ... Obsidian hydration dating is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian. ...

References

  1. ^ http://www.em.gov.bc.ca/mining/GeolSurv/MetallicMinerals/MineralDepositProfiles/profiles/r12.htm
  2. ^ Buck B.A. 1982. Ancient technology in contemporary surgery. The Western Journal of Medicine, 136, 265-269
  3. ^ Comparison of obsidian and surgical steel scalpel Retrieved on 06-01-07

External links


  Results from FactBites:
 
OBSIDIAN (Volcanic Silica Glass) (373 words)
Obsidian has been used by ancient people as a cutting tool, for weapons, and for ceremonial purposes and is sometimes found by archaeologists in excavations.
Obsidian can contain small bubbles of air that are aligned along layers created as the molten rock was flowing just before being cooled.
The piezoelectric and optical properties in quartz are thus absent in obsidian.
USGS Photo Glossary: Obsidian (202 words)
Obsidian is often formed in rhyolite lava flows where the lava cools so fast that crystals do not have time to grow.
The colors in obsidian result from the oxidation state of the chemical elements within the tiny minerals that are finely dispersed in the glass.
Some obsidian is banded, a consequence of oxidation on a flow surface being folded into the lava as it continues to move.
  More results at FactBites »

 
 

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