plus MgO, Fe3O4
|Color||Deep black or blackish green|
|Mohs scale hardness||5–6|
It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. 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 polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which were used in the past in cutting and piercing tools, and it has been used experimentally as surgical scalpel blades.
Origin and properties
... among the various forms of glass we may reckon Obsian glass, a substance very similar to the stone found by Obsius in Ethiopia.
The translation into English of Natural History written by the elder Pliny of Rome shows a few sentences on the subject of a volcanic glass called Obsian, so named from its resemblance to a stone (obsiānus lapis) found in Ethiopia by Obsius, a Roman explorer.
Obsidian is the rock formed as a result of quickly cooled lava, which is the parent material. Tektites were once thought by many to be obsidian produced by lunar 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 complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is usually 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. Having a low water content when newly formed, typically less than 1% water by weight, obsidian becomes progressively hydrated when exposed to groundwater, forming perlite.
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 brown to black color. 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). 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, rainbow-like sheen (rainbow obsidian) is caused by inclusions of magnetite nanoparticles.
Obsidian can be found in locations which have experienced rhyolitic eruptions. It can be found in Argentina, Armenia, Azerbaijan, Australia, Canada, Chile, Georgia, Greece, El Salvador, Guatemala, Iceland, Italy, Japan, Kenya, Mexico, New Zealand, Papua New Guinea, Peru, Scotland, Turkey and the United States. Obsidian flows which may be hiked 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. 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 U.S. states including Arizona, Colorado, New Mexico, Texas, Utah, Washington, Oregon and Idaho. Obsidian can also be found in the eastern U.S. states of Virginia, as well as Pennsylvania and North Carolina.
The first archaeological evidence known of usage were made from within Kariandusi and other sites of the Acheulian age (beginning 1.5 million years previously) dated 700,000 BC, although the number of objects found at these sites were very low relative to the Neolithic. Use of obsidian in pottery of the Neolithic in the area around Lipari was found to be significantly less at a distance representing two weeks journeying. 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. The first attested civilized use is from excavations at Tell Brak dated the late fifth millennia. Obsidian was valued in 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. Modern archaeologists have developed a relative dating system, obsidian hydration dating, to calculate the age of obsidian artifacts.
In the Ubaid in the 5th millennium BC, 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. Obsidian was also used in ritual circumcisions because of its deftness and sharpness. In the eastern Mediterranean area the material was used to make tools, mirrors and decorative objects.
Obsidian has also been found in Gilat, 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 (NAA) on the obsidian found at this site helped to reveal trade routes and exchange networks previously unknown.
Lithic analysis can be instrumental in understanding prehispanic groups in Mesoamerica. A careful analysis of obsidian in a culture or place can be of considerable 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. 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.
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.
Native American people traded obsidian throughout the Americas. 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 Melos, Nisyros or Yiali, islands in the Aegean Sea. Obsidian cores and blades were traded great distances inland from the coast.
Obsidian can be used to make extremely sharp knives, and obsidian blades are a type of glass knife made using naturally occurring instead of manufactured glass. Obsidian is used by some surgeons for scalpel blades although not approved by the US Food and Drug Administration (FDA) for use on humans. Well-crafted obsidian blades, as with any glass knife, can have a cutting edge many times sharper than high-quality steel surgical scalpels, the cutting edge of the blade being only about 3 nanometers thick. Even the sharpest metal knife has a jagged, irregular blade when viewed under a strong enough microscope; when examined even under an electron microscope an obsidian blade is still smooth and even. One study found that obsidian incisions produced fewer inflammatory cells and less granulation tissue at seven days, in a group of rats, although no differences were found after 21 days. Don Crabtree produced obsidian blades for surgery and other purposes, and has written articles on the subject. Obsidian scalpels may currently be purchased for surgical use on research animals.
Obsidian is also used for ornamental purposes and as a gemstone. 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" are small rounded obsidian nuggets often embedded within a grayish-white perlite matrix.
|Wikimedia Commons has media related to:|
- Apache tears
- Hyaloclastite and tachylite – volcanic glasses with basaltic composition
- Libyan desert glass
- Mayor Island / Tuhua - a source of Māori obsidian tools.
- Obsidian hydration dating
- Stone tools
- Yaxchilan Lintel 24 – Ancient carving showing a Maya bloodlet ritual involving a rope with obsidian shards.
- Peter Roger Stuart Moorey (1999). Ancient mesopotamian materials and industries: the archaeological evidence. Eisenbrauns. pp. 108–. ISBN 978-1-57506-042-2.
- Geological Survey (U.S.) (1981). Geological Survey (U.S.). The Survey. pp. 185–.
- Obsidian. Mindat.org
- Brian Cotterell; Johan Kamminga (1992). Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. pp. 127–. ISBN 978-0-521-42871-2. Retrieved 9 September 2011.
- Pliny the Elder (translated by John Bostock, Henry Thomas Riley) (1857). The natural history of Pliny 6. H G Bohn. ISBN 1851099301.
- obsidian. The Concise Oxford Dictionary of English Etymology. Oxford University Press (1996). Retrieved 2011-11-20.
- D Harper. obsidian. Etymology online. 2012-06-17
- M H Manser. The Facts On File Dictionary of Allusions. Infobase Publishing, 2008, ISBN 0816071055.
- M E Malainey. A Consumer's Guide to Archaeological Science: Analytical Techniques, Springer, 2010 ISBN 1441957030
- P L Barnes-Svarney, T E Svarney (2004). The Handy Geology Answer Book. Visible Ink Press. ISBN 1578591562.
- M Martini, M Milazzo, M Piacentini, Società Italiana di Fisica (2004). Physics Methods in Archaeometry 154. IOS Press. ISBN 1586034243.
- "Perlite – Mineral Deposit Profiles, B.C. Geological Survey". Retrieved 2007-11-20.
- Nadin, E. (2007). "The secret lives of minerals" (PDF). Engineering & Science, No. 1, 10-20.
- Bonetti, R., P. Di Cesare, A. Guglielmetti, F. Malerba, E. Migliorini, M. Oddone, J. R. Bird, R. Torrence and R. J. Bultitude, 1998. Fission track dating of obsidian source samples from the Willaumez Peninsula, Papua New Guinea and eastern Australia. Records of the Australian Museum 50(3): 277–284. [25 November 1998]. doi:10.3853/j.0067-1975.50.1998.1286
- Washington Obsidian Source Map. Obsidianlab.com. Retrieved on 2011-11-20.
- Oregon Obsidian Sources. Sourcecatalog.com (2011-11-15). Retrieved on 2011-11-20.
- Iain Morley and Colin Renfrew. The Archaeology of Measurement: Comprehending Heaven, Earth and Time in Ancient Societies, Cambridge University Press, 2010 ISBN 0521119901.
- E Blake, A B Knapp (2005). The Archaeology Of Mediterranean Prehistory. John Wiley & Sons. ISBN 0631232680.
- Prince Mikasa no Miya Takahito. Essays on Anatolian Archaeology, Otto Harrassowitz Verlag, 1993 ISBN 3447033959.
- L Romano. 6 ICAANE, Otto Harrassowitz Verlag, 2010 Volume 3 of Proceedings of the 6th International Congress of the Archaeology of the Ancient Near East: 5–10 May 2009 ISBN 3447062177.
- P R S Moorey. Ancient Mesopotamian Materials and Industries: The Archaeological Evidence Eisenbrauns, 1999 ISBN 1575060426.
- S Bunny. American trade routes for obsidian. New Scientist (1985-04-18).
- D Schmandt-Besserat. Volume 3 of Invited lectures on the Middle East at the University of Texas at Austin, Undena Publications, 1979, ISBN 0890030316
- HV Merrick, FH Brown, WP Nash. Society, Culture, and Technology in Africa, Volume 11, 1994 (Masca Research Papers in Science and Archaeology Supplement) University of Pennsylvania Museum of Archaeology, ISBN 1931707057
- J. D. Fage. The Cambridge history of Africa: From c. 1600 to c. 1790, Part 1050, Cambridge University Press, 1979 ISBN 0521215927
- National Museum of Kenya. Kariandusi. Retrieved 2012-06-30
- A. M. Pollard, Carl Heron (2008). Archaeological Chemistry. Royal Society of Chemistry. ISBN 0854042628.
- Jason A. Ur (2007). "Early Mesopotamian urbanism: a new view from the North" (PDF). Antiquity 81 (313): 585–600.
- John Noble Wilford (2010-04-05). "In Syria, a Prologue for Cities". The New York Times.
- Harrell, James A. (2000). "Stone in Ancient Egypt". University of Toledo.
- George Robert Rapp (2002). Archaeomineralogy. Springer. ISBN 3540425799.
- Yellin, Joseph; Levy, Thomas E.; Rowan, Yorke M. (1996). "New Evidence on Prehistoric Trade Routes: The Obsidian Evidence from Gilat, Israel". Journal of Field Archaeology 23: 361–368. doi:10.1179/009346996791973873.
- Brokmann, Carlos, Tipología y análisis de la obsidiana de Yaxchilán, Chiapas, Colección Científica, no. 422, INAH, 2000
- C. Michael Hogan (2008). Morro Creek, A. Burnham (ed.). Megalithic.co.uk. Retrieved on 2011-11-20.
- Mario Pino Quivido and Rayen Navarro (2005). "Geoarqueología del sitio arcaico Chan-Chan 18, costa de Valdivia: Discriminación de ambientes de ocupación humana y su relación con la transgresión marina del Holoceno Medio". Revista Geológica de Chile 32. doi:10.4067/S0716-02082005000100004.
- Naranjo, José A; Stern, Charles R (2004). "Holocene tephrochronology of the southernmost part (42°30'-45°S) of the Andean Southern Volcanic Zone". Revista geológica de Chile 31 (2): 225–240. doi:10.4067/S0716-02082004000200003. OCLC 61022562.
- Buck, BA (March 1982). "Ancient Technology in Contemporary Surgery". The Western journal of medicine 136 (3): 265–269. PMC 1273673. PMID 7046256.
- Haviland, W.A.; Prins H.E.L.; Walrath D.; McBride B. (2010). Anthropology: The Human Challenge (13 ed.). Cengage Learning. p. 196. ISBN 9780495810841. Retrieved 27 September 2012.
- Disa, JJ (Oct 1993). "A comparison of obsidian and surgical steel scalpel wound healing in rats.". Plastic & Reconstructive Surgery (92). Retrieved 23 September 2015.
- Fine Science Tools (FST). "FST product catalog". FST. Retrieved 7 September 2012.
|Wikimedia Commons has media related to Obsidian.|