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Obsidian () is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from
felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...
lava, rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. It is commonly found within the margins of
rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
lava flows known as obsidian flows. These flows have a high content of silica, granting them a high viscosity. The high viscosity inhibits diffusion of atoms through the lava, which inhibits the first step (
nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...
) in the formation of mineral crystals. Together with rapid cooling, this results in a natural glass forming from the lava. Obsidian is hard, brittle, and
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wi ...
; it therefore
fractures Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...
with sharp edges. In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades.


Origin and properties

The '' Natural History'' by the Roman writer Pliny the Elder includes a few sentences about a volcanic glass called obsidian (''lapis obsidianus''), discovered in Ethiopia by Obsidius, a Roman explorer. Obsidian is formed from quickly cooled lava, which is the parent material. Extrusive formation of obsidian may occur when
felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...
lava cools rapidly at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air. Intrusive formation of obsidian may occur when felsic lava cools along the edges of a
dike Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes, ...
. Tektites were once thought by many to be obsidian produced by
lunar Lunar most commonly means "of or relating to the Moon". Lunar may also refer to: Arts and entertainment * ''Lunar'' (series), a series of video games * "Lunar" (song), by David Guetta * "Lunar", a song by Priestess from the 2009 album ''Prior t ...
volcanic eruptions, though few scientists now adhere to this hypothesis. Obsidian is mineral-like, but not a true mineral because, as a glass, it is not crystalline; in addition, its composition is too variable to be classified as a mineral. It is sometimes classified as a
mineraloid A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amor ...
. Though obsidian is usually dark in color, similar to mafic rocks such as basalt, the composition of obsidian is extremely felsic. Obsidian consists mainly of SiO2 ( silicon dioxide), usually 70% by weight or more. Crystalline rocks with a similar composition include granite and
rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
. Because obsidian is metastable at the Earth's surface (over time the glass devitrifies, becoming fine-grained mineral crystals), obsidian older than Miocene in age is rare. Exceptionally old obsidians include a Cretaceous welded tuff and a partially devitrified Ordovician perlite. This transformation of obsidian is accelerated by the presence of water. Although newly formed obsidian has a low water content, typically less than 1% water by weight, it becomes progressively hydrated when exposed to groundwater, forming perlite. Pure obsidian is usually dark in appearance, though the color varies depending on the impurities present. Iron and other transition elements may give the obsidian a dark brown to black color. Most black obsidians contain nanoinclusions of magnetite, an
iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
. Very few samples of obsidian are nearly colorless. In some stones, the inclusion of small, white, radially clustered crystals (
spherulites In petrology, spherulites () are small, rounded bodies that commonly occur in vitreous igneous rocks. They are often visible in specimens of obsidian, pitchstone, and rhyolite as globules about the size of millet seed or rice grain, with a dul ...
) of the mineral cristobalite in the black glass produce a blotchy or snowflake pattern (''snowflake obsidian''). Obsidian 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''). An
iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...
, rainbow-like sheen (''fire obsidian'') is caused by inclusions of magnetite nanoparticles creating thin-film interference. Colorful, striped obsidian (''rainbow obsidian'') from Mexico contains oriented nanorods of hedenbergite, which cause the rainbow striping effects by thin-film interference.


Occurrence

Obsidian is found near volcanoes in locations which have undergone rhyolitic eruptions. It can be found in Argentina, Armenia, Azerbaijan,
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, Canada, Chile, Georgia, Ecuador,
El Salvador El Salvador (; , meaning " The Saviour"), officially the Republic of El Salvador ( es, República de El Salvador), is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south b ...
, Greece,
Guatemala Guatemala ( ; ), officially the Republic of Guatemala ( es, República de Guatemala, links=no), is a country in Central America. It is bordered to the north and west by Mexico; to the northeast by Belize and the Caribbean; to the east by H ...
, Hungary, Iceland, Italy,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, Kenya, Mexico, New Zealand, Papua New Guinea, Peru, Scotland,
The Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...
, Turkey and the United States. Obsidian flows which may be hiked on are found within the
caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...
s of Newberry Volcano and Medicine Lake Volcano in the
Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...
of western North America, and at Inyo Craters east of the Sierra Nevada in California. Yellowstone National Park has a mountainside containing obsidian located between
Mammoth Hot Springs Mammoth Hot Springs is a large complex of hot springs on a hill of travertine in Yellowstone National Park adjacent to Fort Yellowstone and the Mammoth Hot Springs Historic District. It was created over thousands of years as hot water from the s ...
and the Norris Geyser Basin, and deposits can be found in many other western U.S. states including Arizona, Colorado, New Mexico, Texas, Utah, and Washington, Oregon and Idaho. There are only four major deposit areas in the central Mediterranean: Lipari, Pantelleria,
Palmarola Palmarola is a craggy, mostly uninhabited island in the Tyrrhenian Sea off the west coast of Italy. It is the second-largest of the Pontine Islands and located about west from Ponza. In antiquity it was known as Palmaria. Palmarola has an extr ...
and
Monte Arci The Monte Arci is an isolated massif in the Uras plain in Campidano, south-western Sardinia, Italy. It is composed by three volcanic basalt towers, the highest one reaching an elevation of 812 m. The inner part of the massif is composed of ...
( Sardinia). Ancient sources in the Aegean were Milos and Gyali.
Acıgöl Acıgöl, () formerly Dobada, is a town and district of Nevşehir Province in the Central Anatolia region of Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcon ...
town and the
Göllü Dağ Göllü is a lava dome located in central Turkey. The volcano has produced rhyolite, dacite and basalt. The lavas have been dated at 1.33 to 0.84 million years by fission track dating of obsidian. The dome lies above the Tertiary Derinkuyu calder ...
volcano were the most important sources in central Anatolia, one of the more important source areas in the prehistoric Near East.


Prehistoric and historical use

The first known archaeological evidence of usage was in
Kariandusi Kariandus is a settlement in Nakuru County, Kenya. It is located 17.5 miles from Nakuru town and 7.5 miles from Gilgil town. Human presence in the area dates back to the stone age. The present inhabitants of Kariandusi settled in the area in ea ...
(Kenya) and other sites of the
Acheulian Acheulean (; also Acheulian and Mode II), from the French ''acheuléen'' after the type site of Saint-Acheul, is an archaeological industry of stone tool manufacture characterized by the distinctive oval and pear-shaped "hand axes" associated ...
age (beginning 1.5 million years BP) dated 700,000 BC, although only very few objects have been found at these sites relative to the Neolithic. Manufacture of obsidian bladelets at Lipari had reached a high level of sophistication by the late Neolithic, and was traded as far as Sicily, the southern Po river valley, and Croatia. Obsidian bladelets were used in ritual circumcisions and cutting of umbilical cords of newborns. Anatolian sources of obsidian are known to have been the material used in the Levant and modern-day Iraqi Kurdistan from a time beginning sometime about 12,500 BC. Obsidian artifacts are common at Tell Brak, one of the earliest Mesopotamian urban centers, dating to the late fifth millennium BC. Obsidian was valued in
Stone Age The Stone Age was a broad prehistoric period during which stone was widely used to make tools with an edge, a point, or a percussion surface. The period lasted for roughly 3.4 million years, and ended between 4,000 BC and 2,000 BC, with t ...
cultures because, like flint, it could be fractured to produce sharp blades or arrowheads in a process called knapping. Like all glass and some other naturally occurring rocks, obsidian breaks with a characteristic
conchoidal fracture Conchoidal fracture describes the way that brittle materials break or fracture when they do not follow any natural planes of separation. Mindat.org defines conchoidal fracture as follows: "a fracture with smooth, curved surfaces, typically slig ...
. It was also polished to create early mirrors. Modern
archaeologists Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
have developed a relative dating system,
obsidian hydration dating Obsidian hydration dating (OHD) is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian. Obsidian is a volcanic glass that was used by prehistoric people as a raw material in the manufacture ...
, to calculate the age of obsidian
artifact Artifact, or artefact, may refer to: Science and technology * Artifact (error), misleading or confusing alteration in data or observation, commonly in experimental science, resulting from flaws in technique or equipment ** Compression artifact, a ...
s.


Europe

Obsidian artifacts first appeared in the European continent in Central Europe in the
Middle Paleolithic The Middle Paleolithic (or Middle Palaeolithic) is the second subdivision of the Paleolithic or Old Stone Age as it is understood in Europe, Africa and Asia. The term Middle Stone Age is used as an equivalent or a synonym for the Middle Paleoli ...
and had become common by the Upper Paleolithic, although there are exceptions to this. Obsidian played an important role in the transmission of Neolithic knowledge and experiences. The material was mainly used for production of
chipped tools A microchip implant is an identifying integrated circuit placed under the skin of an animal. The chip, about the size of a large grain of rice, uses passive radio-frequency identification (RFID) technology, and is also known as a PIT (passive i ...
which were very sharp due to its nature. Artifacts made of obsidian can be found in many Neolithic cultures across Europe. The source of obsidian for cultures inhabiting the territory of and around Greece was the island of Milos; the
Starčevo–Körös–Criș culture The Starčevo–Karanovo I-II–Körös culture or Starčevo–Körös–Criș culture is a grouping of two related Neolithic archaeological cultures in Southeastern Europe: the Starčevo culture and the Körös or Criș culture. Settlements ...
obtained obsidian from sources in Hungary and Slovakia, while the Cardium-Impresso cultural complex acquired obsidian from the island outcrops of the central Mediterranean. Through trade, these artifacts ended up in lands thousands of kilometers away from the original source; this indicates that they were a highly valued commodity.
John Dee John Dee (13 July 1527 – 1608 or 1609) was an English mathematician, astronomer, astrologer, teacher, occultist, and alchemist. He was the court astronomer for, and advisor to, Elizabeth I, and spent much of his time on alchemy, divinatio ...
had a mirror, made of obsidian, which was brought from Mexico to Europe between 1527 and 1530 after Hernando Cortés's conquest of the region.


Middle East and Asia

In the Ubaid in the
5th millennium BC The 5th millennium BC spanned the years 5000 BC to 4001 BC (c. 7 ka to c. 6 ka). It is impossible to precisely date events that happened around the time of this millennium and all dates mentioned here are estimates mostly based on geological an ...
, blades were manufactured from obsidian extracted from outcrops located in modern-day Turkey. Ancient Egyptians used obsidian imported from the eastern Mediterranean and southern Red Sea regions. In the eastern Mediterranean area the material was used to make tools, mirrors and decorative objects. The use of obsidian tools was present in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
near areas of volcanic activity. Obsidian was mined during the
Jōmon period The is the time in Japanese history, traditionally dated between   6,000–300 BCE, during which Japan was inhabited by a diverse hunter-gatherer and early agriculturalist population united through a common Jōmon culture, which reached a c ...
. Obsidian has also been found in
Gilat Gilat ( he, גִּילַת, , Joy) is a moshav in southern Israel. Located in the western Negev desert between Beersheba and Ofakim, it falls under the jurisdiction of Merhavim Regional Council. In it had a population of . History The moshav ...
, a site in the western Negev in Israel. Eight obsidian artifacts dating to the Chalcolithic Age found at this site were traced to obsidian sources in Anatolia.
Neutron activation analysis Neutron activation analysis (NAA) is the nuclear process used for determining the concentrations of elements in many materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on atomic ...
(NAA) on the obsidian found at this site helped to reveal trade routes and exchange networks previously unknown.


Americas

Lithic analysis helps to understand pre-hispanic groups in Mesoamerica. A careful analysis of obsidian in a culture or place can be of considerable use to reconstruct commerce, production, and 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. Another example is the archeological recovery at coastal Chumash sites in California, indicating considerable trade with the distant site of Casa Diablo, California in the
Sierra Nevada Mountains The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley (California), Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Cars ...
. 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 could inflict terrible injuries, combining the sharp cutting edge of an obsidian blade with the ragged cut of a serrated weapon. The polearm version of this weapon was called ''
tepoztopilli The ''tepoztopilli'' was a common front-line weapon of the Aztec military. The tepoztopilli was a pole-arm, and to judge from depictions in various Aztec codices it was roughly the height of a man, although historian John Pohl indicates that the ...
''. Obsidian mirrors were used by some Aztec priests to conjure visions and make prophecies. They were connected with Tezcatlipoca, god of obsidian and sorcery, whose name can be translated from the Nahuatl language as 'Smoking Mirror’. Native American people traded obsidian throughout the Americas. Each volcano and in some cases each volcanic eruption produces a distinguishable type of obsidian, allowing archaeologists to trace the origins of a particular artifact. Similar tracing techniques have also allowed obsidian in Greece to be identified as coming from Milos,
Nisyros Nisyros also spelled Nisiros ( el, Νίσυρος, Nísiros) is a volcanic Greek island and municipality located in the Aegean Sea. It is part of the Dodecanese group of islands, situated between the islands of Kos and Tilos. Its shape is appro ...
or Gyali, islands in the Aegean Sea. Obsidian cores and blades were traded great distances inland from the coast. In Chile obsidian tools from
Chaitén Volcano Chaitén (, ) is a Chilean town, commune and former capital of the Palena Province in Los Lagos Region. The town is north of the mouth of Yelcho River, on the east coast of the Gulf of Corcovado. The town is strategically close to the northern end ...
have been found as far away as in Chan-Chan north of the volcano, and also in sites 400 km south of it.


Oceania

The Lapita culture, active across a large area of the Pacific Ocean around 1000 BC, made widespread use of obsidian tools and engaged in long distance obsidian trading. The complexity of the production technique for these tools, and the care taken in their storage, may indicate that beyond their practical use they were associated with prestige or high status. 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), which were encircled by rings of bird bone. Obsidian was used to inscribe the Rongorongo glyphs.


Current use

Obsidian can be used to make extremely sharp knives, and obsidian blades are a type of
glass knife A glass knife is a knife with a blade made of glass, with a fracture line forming an extremely sharp cutting edge. Glass knives were used in antiquity due to their natural sharpness and the ease with which they could be manufactured. In modern e ...
made using naturally occurring obsidian instead of manufactured glass. Obsidian is used by some surgeons for scalpel blades, although this is not approved by the US Food and Drug Administration (FDA) for use on humans. Well-crafted obsidian blades, like any glass knife, can have a cutting edge many times sharper than high-quality steel surgical scalpels: the cutting edge of the blade is only about three nanometers thick. All metal knives have a jagged, irregular blade when viewed under a strong enough microscope; however, obsidian blades are still smooth, even when examined under an electron microscope. One study found that obsidian incisions produced fewer
inflammatory cell White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...
s and less granulation tissue in a group of rats after seven days but the differences disappeared after twenty-one days.
Don Crabtree Don E. Crabtree (June 8, 1912 – November 16, 1980) was an American flintknapper and pioneering experimental archaeologist. Known as the "dean of American flintknappers" he was mostly self-educated, however he was awarded an honorary doct ...
has produced surgical obsidian blades and written articles on the subject. Obsidian scalpels may currently be purchased for surgical use on
research animals Research is " creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization and analysis of evidence to increase understanding of a topic, characterized by a particular attentiveness ...
. The major disadvantage of obsidian blades is their brittleness compared to those made of metal, thus limiting the surgical applications for obsidian blades to a variety of specialized uses where this is not a concern. Obsidian is also used for ornamental purposes and as a
gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
. It presents a different appearance depending on how it is cut: in one direction it is jet black, while in another it is glistening gray. "
Apache tears Apache tears are rounded pebbles of obsidian or "obsidianites" composed of black or dark-colored natural volcanic glass, usually of rhyolitic composition and bearing conchoidal fracture. Also known by the lithologic term marekanite, this variety ...
" are small rounded obsidian nuggets often embedded within a grayish-white perlite
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
.
Plinths A pedestal (from French ''piédestal'', Italian ''piedistallo'' 'foot of a stall') or plinth is a support at the bottom of a statue, vase, column, or certain altars. Smaller pedestals, especially if round in shape, may be called socles. In ...
for audio turntables have been made of obsidian since the 1970s, such as the grayish-black SH-10B3 plinth by Technics.


See also

* * * and
tachylite Tachylite ( ; also spelled tachylyte) is a form of basaltic volcanic glass. This glass is formed naturally by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is chemical decomposition, decomposable by acids and readi ...
– volcanic glasses with basaltic composition * * * - a source of Māori obsidian tools * * * – Ancient carving showing a Maya bloodlet ritual involving a rope with obsidian shards.


Footnotes


References


External links


USGS Obsidian photo glossary
{{Authority control * Gemstones Vitreous rocks Volcanology