Obsidian
Volcanic glass used for sharp tools since prehistory.
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When lava from a volcano cools quickly and crystals have little chance to grow, the resulting natural glass is called obsidian.[1] The amorphous, hard, and brittle nature of obsidian causes it to break producing extremely sharp edges.[2]
Key facts and history
The first known archaeological evidence of obsidian usage was in Kariandusi, Kenya, at Acheulian sites dated to 700,000 BC.[3] In his work Natural History, the Roman author Pliny the Elder wrote about a volcanic glass termed obsidian (lapis obsidianus), which he said was found in Ethiopia by the explorer Obsidius.[4] Obsidian flows, which are rhyolitic lava flows, typically have obsidian located along their margins.[5] Because these lava flows contain a high percentage of silica, their viscosity is high, which slows atomic diffusion and prevents the nucleation step needed for crystal formation.[5]
The combination of this high viscosity and rapid cooling leads to the lava forming a natural glass.[5] Obsidian does not qualify as a true mineral because it lacks a crystalline structure and its chemical makeup varies too widely to fit mineral classification.[6]
What the cited sources add
A CNN article reports that obsidian can produce cutting edges many times finer than the best steel scalpels, with an edge as fine as 30 angstroms.[7] The Hopewell Culture National Historical Park website states that obsidian artifacts found in Ohio came from Obsidian Cliff in Wyoming and Bear Gulch in Idaho, traced through X-ray fluorescence.[8] That website also describes a large obsidian spear point over 17 inches long found in the Hopewell Mound Group.[8] A study of obsidian at Morro Creek showed that materials derived from the Napa, Coso, Casa Diablo, and Bodie Hills sites, with Coso representing the greatest abundance.[9]
The same article mentions that Dr. Lee Green, who is a professor and chairman of the Department of Family Medicine at the University of Alberta, regularly employs obsidian blades, citing benefits like faster healing and reduced scarring.[7]
References
- Wikipedia, "Obsidian" (CC BY-SA 4.0) en.wikipedia.org
- Wikipedia, "Obsidian" (CC BY-SA 4.0), which cites: "Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture", Cambridge University Press, 1992, p. 127– (we also read that source) en.wikipedia.org
- Wikipedia, "Obsidian" (CC BY-SA 4.0), which cites: Bunny, "Ancient trade routes for obsidian", New Scientist, April 18, 1985; Schmandt-Besserat, "Early technologies", Undena Publications, 1979; Merrick, "Society, Culture, and Technology in Africa Import.", Univ Museum Pubns, 1994; J. D. Fage. The Cambridge history of Africa: From c. 1600 to c. 1790, Part 1050, Cambridge University Press, 1979; National Museum of Kenya. Kariandusi . Retrieved June 30, 2012; Martinelli, "Lipari (Aeolian islands) obsidian in the late Neolithic. Artifacts, supply, and function", Open Archaeology, April 20, 2019, p en.wikipedia.org
- Wikipedia, "Obsidian" (CC BY-SA 4.0), which cites: Dictionary of Greek and Roman Biography and Mythology, vol. III, p. 2 ("Obsidius").; obsidian. The Concise Oxford Dictionary of English Etymology. Oxford University Press (1996). Retrieved November 20, 2011.; D Harper. obsidian. Etymology online. June 17, 2012; M H Manser. The Facts On File Dictionary of Allusions. Infobase Publishing, 2008, . (original not read by us) en.wikipedia.org
- Wikipedia, "Obsidian" (CC BY-SA 4.0), which cites: Raymond, "Petrology : the study of igneous, sedimentary, metamorphic rocks", Wm. C. Brown, 1995, p. 27 (we also read that source) en.wikipedia.org
- Wikipedia, "Obsidian" (CC BY-SA 4.0), which cites: "Handbook of Soil Sciences: Properties and Processes", CRC Press, 2012, p. 20–24 (we also read that source) en.wikipedia.org
- Shadbolt, "CNN Health: How Stone Age blades are still cutting it in modern surgery", CNN, April 2, 2015. facts only, no text reused. cnn.com
- "Hopewell Culture Obsidian", nps.gov. facts only, no text reused. nps.gov
- Hogan, "Morro Creek", Megalithic.co.uk, 2008. facts only, no text reused. megalithic.co.uk
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Obsidian (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Obsidian (CC BY-SA 4.0).
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