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. Lake County is a county located in the US state of Oregon. It is so named for the sizeable number of lakes found within its boundaries including A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken Conchoidal Fracture describes the way that Brittle materials break when they do not follow any natural planes of separation. The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material 5
Luster	Vitreous
Optical Properties	Translucent
Specific gravity	~ 2. Lustre (or 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 (also called pellucidity) is the Material property of allowing Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 6

Obsidian is a naturally occurring glass formed as an extrusive igneous rock. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many It is produced when felsic lava extruded from a volcano cools without crystal growth. Felsic is a term used in Geology to refer to Silicate minerals, Magma, and rocks which are enriched in the lighter elements such as Silicon Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Plate tectonics and hotspots Divergent plate boundaries At the Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerisation degree of the lava. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. 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. In Archaeology, a projectile point is an object that was hafted and used either as Knife or Projectile tip or both commonly called an Arrowhead A scalpel is a small but extremely sharp knife used for Surgery, anatomical Dissection, and various Arts and crafts. ^[1]

Origin and properties

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. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating It is sometimes classified as a mineraloid. A mineraloid is a Mineral -like substance that does not demonstrate Crystallinity. Though obsidian is dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Mafic is an adjective describing a Silicate mineral or rock that is rich in magnesium and iron the term was derived by contracting "magnesium" and "ferric" Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Felsic is a term used in Geology to refer to Silicate minerals, Magma, and rocks which are enriched in the lighter elements such as Silicon Obsidian consists mainly of SiO₂ (silicon dioxide), usually 70% or more. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Crystalline rocks with obsidian's composition include granite and rhyolite. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. 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. 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 The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of This breakdown of obsidian is accelerated by the presence of water. Obsidian has a low water content when fresh, typically less than 1% water by weight ^[2], but becomes progressively hydrated when exposed to groundwater, forming perlite. Perlite is an Amorphous Volcanic Glass that has a relatively high Water content typically formed by the hydration of Obsidian Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Tektites (from Greek tektos, molten are natural Glass objects up to a few centimeters in size which most scientists argue were formed by the impact of

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. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 A very few samples are nearly colorless. 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). In mineralogy an inclusion is any material that is trapped inside a Mineral during its formation The mineral cristobalite is a high-temperature polymorph of Quartz and Tridymite. 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 (sheen obsidian) or a rainbow sheen (rainbow obsidian).

Glass Mountain, a large obsidian flow at Medicine Lake Volcano. Medicine Lake Volcano is a large Shield volcano in northeastern California about northeast of Mount Shasta.

Counterclockwise from top: obsidian, pumice and rhyolite (light color)

Occurrence

Obsidian can be found in locations which have experienced rhyolitic eruptions. Pumice is a textural term for a volcanic rock that is a solidified frothy lava composed of highly microvesicular glass Pyroclastic with very thin translucent This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Obsidan flows which you can hike on 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. Newberry Volcano is a large Shield volcano located east of the Cascade Range and about southeast of Bend Oregon. Medicine Lake Volcano is a large Shield volcano in northeastern California about northeast of Mount Shasta. Mono-Inyo Craters in California USA are a nearly straight line of small Volcanoes that stretch from Mammoth Mountain and Long Valley Caldera California ( is a US state on the West Coast of the United States, along the Pacific Ocean. Yellowstone National Park has a mountainside containing obsidian located between Mammoth Hot Springs and the Norris Geyser Basin, and deposits can be found in many other western US states including Arizona, Colorado, Texas, Utah, Oregon and Idaho. The geothermal areas of Yellowstone include several Geyser basins in Yellowstone National Park as well as other geothermal features such as Hot The geothermal areas of Yellowstone include several Geyser basins in Yellowstone National Park as well as other geothermal features such as Hot The State of Arizona ( is a state located in the southwestern region of the United States. The State of Colorado ( or chiefly by nonresidents) is a state located in the Rocky Mountain region of the United States of America. Texas ( is a state geographically located in the South Central United States and is also known as the Lone Star State. The State of Utah (ˈjuːtɔː or) is a western state of the United States. Oregon ( is a state in the Pacific Northwest region of the United States. The State of Idaho ( is a state in the Pacific Northwest region of the United States of America. Obsidian can also be found in Armenia, Turkey, Italy, Mexico, Iceland, Greece and Scotland. Armenia (Հայաստան transliterated: Hayastan,) officially the Republic of Armenia (Հայաստանի Հանրապետություն Hayastani Turkey (Türkiye known officially as the Republic of Turkey ( is a Eurasian Country that stretches Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( Greece (Ελλάδα transliterated: Elláda, historically, Ellás,) officially the Hellenic Republic (Ελληνική Δημοκρατία Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain.

Historical use

Obsidian arrowhead. An arrowhead is point of an Arrow, or a shape resembling such a point as Archaeological artifacts arrowheads are a subclass of Projectile points

Obsidian was valued in Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads. The Stone Age is a broad prehistoric time period during which Humans widely used stone for toolmaking Flint (or flintstone) is a hard sedimentary Cryptocrystalline form of the Mineral Quartz, categorized as a variety of Chert Like all glass and some other types of naturally occurring rocks, obsidian breaks with a characteristic conchoidal fracture. Conchoidal Fracture describes the way that Brittle materials break when they do not follow any natural planes of separation. It was also polished to create early mirrors. A mirror is an object with a surface that has good Specular reflection; that is it is smooth enough to form an Image.

Pre-Columbian Mesoamericans' use of obsidian was extensive and sophisticated, including carved and worked obsidian for tools and decorative objects. The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences Mesoamerica or Meso-America (Mesoamérica is a Region extending approximately from central Mexico to Honduras and Nicaragua, defined Obsidian is a naturally formed Volcanic Glass that was an important part of the Material culture of Pre-Columbian Mesoamerica A broader definition of a tool is an entity used to interface between two or more domains that facilitates more effective action of one domain upon the other 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 macuahuitl (a name derived from the Nahuatl language) is a Weapon shaped like a wooden club Lithic analysis can be instrumental in understanding prehispanic groups in Mesoamerica. A careful analysis of obsidian in a culture or place can be of use to reconstruct commerce, production, distribution and thereby understand economic, social and political aspects of a civilization. This is the case in Yaxchilán, a maya city where even warfare implications have been studied linked with obsidian use and its debris. Yaxchilan (also sometimes historically referred to by the names Menché and City Lorillard) is an ancient Maya city located on the Usumacinta River ^[3]

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. Milos (in Greek, Μήλος &mdash not related to the modern word μήλο &ndash milo " Apple " Nisyros (Νίσυρος also transliterated Nissiros) is a volcanic Greek island and municipality located in the Aegean Sea. Gyali (Γυαλί " Glass " also spelled Yiali or Yali; pronounced) is a volcanic Greek Island in the Etymology In ancient times there were various explanations for the name Aegean. Obsidian cores and blades were traded great distances inland from the coast.

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). Moai (or mo‘ai) (ˈmoʊаɪ are Monolithic human figures carved from rock on the Polynesian island of Rapa Nui (Easter Island

Modern archaeologists have developed a dating system Obsidian hydration dating to calculate the age of Obsidian artifacts. Archaeology, archeology, or archæology (from Greek grc ἀρχαιολογία archaiologia – grc ἀρχαῖος archaīos 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 markings are spherulites. Spherulites, in Petrology, are small rounded bodies that commonly occur in Vitreous Igneous rocks They are often visible in specimens of Obsidian

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 nanometres wide ^[4]. Cardiac surgery is Surgery on the Heart and/or Great vessels performed by a Cardiac surgeon. A scalpel is a small but extremely sharp knife used for Surgery, anatomical Dissection, and various Arts and crafts. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a 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. Granulation tissue is the perfused, fibrous connective tissue that replaces a Fibrin clot in healing wounds. ^[5]

Obsidian is also used for ornamental purposes and as a gemstone. A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash It possesses the 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. Perlite is an Amorphous Volcanic Glass that has a relatively high Water content typically formed by the hydration of Obsidian

See also

• Amorphism
• Flint knapping
• Hyaloclastite and tachylite - volcanic glasses with basaltic composition
• Obsidian hydration dating
• Obsidian use in Mesoamerica
• Volcanic glass
• Yaxchilan Lintel 24 - Ancient carving showing a Maya bloodletting ritual involving a rope with obsidian shards. An Amorphism, in Chemistry, Crystallography and by extension to other areas of the natural sciences is a substance or feature that lacks an ordered form A knapper is a person who shapes Flint, Chert, Obsidian or other stone through the process of knapping or Lithic reduction to manufacture Hyaloclastite is a hydrated Tuff -like Breccia rich in black Volcanic glass, formed during volcanic eruptions under water or under ice Tachylite (also spelled tachylyte is a Vitreous form of Basaltic Volcanic glass. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Obsidian hydration dating is a geochemical method of determining age in either absolute or relative terms of an Artifact made of Obsidian. Obsidian is a naturally formed Volcanic Glass that was an important part of the Material culture of Pre-Columbian Mesoamerica Volcanic glass can refer to any of several types of Vitreous Igneous rocks Most commonly it refers to Obsidian, a Rhyolitic Lintel 24 is the designation given by modern archaeologists to an ancient Maya limestone carving from Yaxchilan, in modern Chiapas, Mexico.

References

External links

• USGS Obsidian photo glossary
• Jim Miller, Obsidian is Hot Stuff, Volcano World
• Obsidian: Mineral galleries
• Mindat with location data
• Obsidian is not a rapidly cooled lava ! (in french)