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CategoryVolcanic glass
(repeatin unit)
70–75% SiO2,
plus MgO, Fe3O4
ColourDeep black
Mohs scale haurdness5–6[1]
Speceefic gravity~2.4[2]
Optical propertiesLeamin

Obsidian is a naiturally occurrin volcanic gless furmed as an extrusive igneous rock.

It is produced whan felsic lava extrudit frae a volcano cuils swith wi meenimum creestal growthe. Obsidian is commonly foond athin the mairgins o rhyolitic lava pirrs kent as obsidian flows, whaur the chemical composeetion (heich silica content) induces a heich viscosity an polymerisation degree o the lava. The inhibeetion o atomic diffusion throu this heich viscous an polymerised lava explicates the lack o creestal growthe. Obsidian is haird an brickle; it fracturs wi vera jaggie rands, that haed been uised in the past in cuttin an piercin tuils, an haes been uised experimentally as surgical scalpel blads.[4]

References[eedit | eedit soorce]

  1. Peter Roger Stuart Moorey (1999). Ancient mesopotamian materials and industries: the archaeological evidence. Eisenbrauns. pp. 108–. ISBN 978-1-57506-042-2.
  2. Geological Survey (U.S.) (1981). Geological Survey (U.S.). The Survey. pp. 185–.
  3. Obsidian. Mindat.org
  4. 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.