Obsidian

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Obsidian
Translucent
Other characteristicsTexture: Smooth; glassy
References[4]

Obsidian (/əbˈsɪdi.ən, ɒb-/ əb-SID-ee-ən ob-)[5] is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.[6]

Obsidian is produced from

crystals. Together with rapid cooling, this results in a natural glass forming from the lava.[7]

Obsidian is hard,

amorphous; it therefore fractures 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.[8]

Origin and properties

Obsidian talus at Obsidian Dome, California
Polished snowflake obsidian, formed through the inclusion of cristobalite crystals

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.[9][10][11][12]

Obsidian is formed from quickly cooled lava, which is the parent material.[13][14][15] Extrusive formation of obsidian may occur when felsic 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.[16][17]

Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions,[18] though few scientists now adhere to this hypothesis.[19]

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.[20] 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. 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.[21] 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,[22] 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

spherulites) 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, rainbow-like sheen (fire obsidian) is caused by inclusions of magnetite nanoparticles creating thin-film interference.[24] Colorful, striped obsidian (rainbow obsidian) from Mexico contains oriented nanorods of hedenbergite, which cause the rainbow striping effects by thin-film interference.[23]

Occurrence

Glass Mountain, a large obsidian flow at Medicine Lake Volcano in California

Obsidian is found near volcanoes in locations which have undergone rhyolitic eruptions. It can be found in Argentina,

Norris Geyser Basin, and deposits can be found in many other western U.S. states including Arizona, Colorado, New Mexico, Texas, Utah, and Washington,[26] Oregon[27] and Idaho
.

There are only four major deposit areas in the central Mediterranean: Lipari, Pantelleria, Palmarola and Monte Arci (Sardinia).[28]

Ancient sources in the Aegean were Milos and Gyali.[29]

Acıgöl town and the Göllü Dağ volcano were the most important sources in central Anatolia, one of the more important source areas in the prehistoric Near East.[30][31][32]

Prehistoric and historical use

Obsidian arrowhead

The first known archaeological evidence of usage was in

archaeologists have developed a relative dating system, obsidian hydration dating, to calculate the age of obsidian artifacts
.

Europe

Obsidian artifacts first appeared in the European continent in Central Europe in the

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.[42] John Dee 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.[43]

Middle East and Asia

Obsidian tools from Tilkitepe, Turkey, 5th millennium BC. Museum of Anatolian Civilizations

In the Ubaid in the 5th millennium BC, blades were manufactured from obsidian extracted from outcrops located in modern-day Turkey.[44] 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.[45]

The use of obsidian tools was present in Japan near areas of volcanic activity.[46][47] Obsidian was mined during the Jōmon period.

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.[48]

Americas

Museo de Arte Popular, Mexico City
.

Sierra Nevada.[50]

Raw obsidian and obsidian blades from the Mayan site of Takalik Abaj

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
.

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'.[43]

Obsidian imported from Milos, found in Minoan Crete

Indigenous people traded obsidian throughout the Americas. Each volcano and in some cases each volcanic eruption produces a distinguishable type of obsidian allowing archaeologists to use methods such as non-destructive energy dispersive X-ray fluorescence to select minor element compositions from both the artifact and geological sample to trace the origins of a particular artifact.[51] Similar tracing techniques have also allowed obsidian in Greece to be identified as coming from Milos, Nisyros or Gyali, islands in the Aegean Sea. Obsidian cores and blades were traded great distances inland from the coast.[52]

In Chile obsidian tools from

Chaitén Volcano have been found as far away as in Chan-Chan 400 km (250 mi) north of the volcano, and also in sites 400 km south of it.[53][54]

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.[55]

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.[56] 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

inflammatory cells and less granulation tissue in a group of rats after seven days but the differences disappeared after twenty-one days.[60] Don Crabtree has produced surgical obsidian blades and written articles on the subject.[58] Obsidian scalpels may be purchased for surgical use on research animals.[61]

The major disadvantage of obsidian blades is their brittleness compared to those made of metal,[62] thus limiting the surgical applications for obsidian blades to a variety of specialized uses where this is not a concern.[58]

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

Obsidian is also used for ornamental purposes and as a gemstone.[63] 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.

Plinths for audio turntables have been made of obsidian since the 1970s, such as the grayish-black SH-10B3 plinth by Technics.

See also

  • Apache tears – Popular term for pebbles of obsidian
  • Helenite – Artificial glass made from volcanic ash
  • basaltic
    composition
  • Knapping – Shaping of conchoidal fracturing stone to manufacture stone tools
  • Libyan desert glass – Desert glass found in Libya and Egypt
  • Mayor Island / Tūhua – New Zealand shield volcano – a source of Māori obsidian tools
  • Obsidian hydration dating – Geochemical dating method
  • Stone tool – Any tool, partially or entirely, made out of stone
  • Vitrophyre – Glassy volcanic rock
  • Yaxchilan Lintel 24 – Ancient Maya limestone carving from Yaxchilan in modern Chiapas, Mexico – Ancient carving showing a Maya bloodlet ritual involving a rope with obsidian shards.

References

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  9. ^ Dictionary of Greek and Roman Biography and Mythology, vol. III, p. 2 ("Obsidius").
  10. ^ obsidian. The Concise Oxford Dictionary of English Etymology. Oxford University Press (1996). Retrieved 2011-11-20.
  11. ^ D Harper. obsidian. Etymology online. 2012-06-17
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  23. ^ Nadin, E. (2007). "The secret lives of minerals" (PDF). Engineering & Science (1): 10–20.
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  25. ^ Washington Obsidian Source Map Archived 2015-08-21 at the Wayback Machine. Obsidianlab.com. Retrieved on 2011-11-20.
  26. ^ Oregon Obsidian Sources. Sourcecatalog.com (2011-11-15). Retrieved on 2011-11-20.
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  28. ^ E Blake; A B Knapp (2005). The Archaeology Of Mediterranean Prehistory. John Wiley & Sons. .
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  32. ^ Bunny, Sarah (18 April 1985). "Ancient trade routes for obsidian". New Scientist.
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  35. ^ National Museum of Kenya. Kariandusi Archived 2007-10-24 at the Wayback Machine. Retrieved 2012-06-30
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  40. ^ Tripković, Boban (2003). "The Quality and Value In Neolithic Europe: An Alternative View on Obsidian Artifacts". South Eastern Europe Proceedings of the ESF Workshop, Sofia. 103: 119–123. Retrieved 21 June 2019.
  41. ^ a b "John Dee's spirit mirror – The British Library". 2020-04-01. Archived from the original on 2020-04-01. Retrieved 2020-04-01.
  42. ^ John Noble Wilford (2010-04-05). "In Syria, a Prologue for Cities". The New York Times.
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  45. doi:10.7152/bippa.v27i0.11982 (inactive 2024-01-22). Retrieved 2 March 2022.{{cite journal}}: CS1 maint: DOI inactive as of January 2024 (link
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  47. ^ Brokmann, Carlos (2000). "Tipología y análisis de la obsidiana de Yaxchilán, Chiapas". Colección Científica (in Spanish). INAH (422).
  48. ^ Hogan, CM (2008). A. Burnham (ed.). "Morro Creek". Megalithic.co.uk. Retrieved 2011-11-20.
  49. ^ Panich, Lee; Michelini, Antonio; Shackley, M. (2012-12-01). "Obsidian Sources of Northern Baja California: The Known and the Unknown". Faculty Publications.
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  55. ^ Shadbolt, Peter (2015-04-02). "CNN Health: How Stone Age blades are still cutting it in modern surgery". CNN. Retrieved 2023-09-07.
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  59. ^ Fine Science Tools (FST). "FST product catalog". FST. Retrieved 7 September 2012.
  60. ^ "Fine Science Tools – Obsidian Scalpels" https://www.finescience.com/en-US/Products/Scalpels-Blades/Micro-Knives/Obsidian-Scalpels
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External links