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|Colour:||black, bluish, mahogany, ...|
Volcanic glass - a rock rather than a mineral, it is a mixture of cryptocrystalline grains of silica minerals in a glass-like suspension, a super-cooled liquid. Obsidian is formed in the latest stage of volcanic eruptions, the silicas left over after most of the other elements and water have been used up are ejected or flow out and rapidly chilled at surface temperatures.
Note on "Transparent/Translucent Obsidian":
A lot of gem-quality water-clear variously coloured 'obsidian' has been offered for sale on the internet (in particular on auction websites) with a variety of sources listed. The material offered for sale is in fact an artificial glass mass-produced in places such as Indonesia.
Visit gemdat.org for gemological information about Obsidian. Currently in public beta-test.
Classification of Obsidian
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Physical Properties of Obsidian
|Colour:||black, bluish, mahogany, golden, peacock, etc. - the colors due largely to refraction by microscopic bubbles (and microscopic mineral inclusions such as magnetit in "Rainbow Obsidian").|
Other Names for Obsidian
|Health Warning:||Obsidian is a natural glass and may have razor-sharp edges that can easily cut skin and flesh. Handle with care. Do not grind dry since long-term exposure to finely ground powder may lead to silicosis.|
References for Obsidian
Stevenson, R.J., Dingwell, D.B., Webb,S.L., and Bagdassarov, N.S. (1995) The equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid-glass transition in volcanic processes. Journal Volcan. Geotherm. Res.: 68: 297-306.
F. Eder, C. Neelmeijer, N. Pearce, M. Bichler, J.H. Sterba, T. Ntaflos, S. Merchel (2013): Volcanic glass under fire - a comparison of three complementary analytical methods. X-Ray Spectrometry, 42, 412-422.
http://members.peak.org/~obsidian/index.html (International Association for Obsidian Studies)
Mindat.org articles about Obsidian
Internet Links for Obsidian
Localities for Obsidian
The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
(TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
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Locality Updated: Wheal Mithian, Mithian, St Agnes, St Agnes District, Cornwall, England, UKFrom Peter Haas, 31st Aug 2014 00:06:07