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Obsidian

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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").
Lustre:
Vitreous
Glassy, fresh igneous rocks with a high silica content and conchoidal fracture

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.


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Classification of ObsidianHide

Sub-divisions of ObsidianHide

Mineralogy of ObsidianHide

Essential minerals - these are minerals that are required within the classification of this rock:
GlassAn amorphous, homogeneous material with a random liquid-like structure generally formed due to rapid cooling.

Physical Properties of ObsidianHide

Vitreous
Transparency:
Translucent
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").
Fracture:
Conchoidal

Synonyms of ObsidianHide

Other Language Names for ObsidianHide

Simplified Chinese:火山玻璃
Spanish:Œqinolita

Varieties of ObsidianHide

Fire ObsidianAn iridescent variety of obsidian. Its 'fire' is caused by thin layers of microcrystals of magnetite (which are approximately the thickness of a wavelength of light). The colour of Rainbow Obsidian occurs from a much thicker volume of the specimen (Nadin,...
Mahogany Obsidian
Rainbow ObsidianObsidian with multicolored iridescence caused by inclusions of magnetite nanoparticles (Nadin, 2007).
Sheen ObsidianA variety of obsidian exhibiting a golden sheen effect.
Snowflake ObsidianA rock - a natural volcanic glass containing white 'snowflake' crystal patterns of the mineral cristobalite, originated due to partial crystallisation of the glass.

Common AssociatesHide

Associated Minerals Based on Photo Data:
Cristobalite49 photos of Obsidian associated with Cristobalite on mindat.org.
Apache Tears27 photos of Obsidian associated with Apache Tears on mindat.org.
Fayalite14 photos of Obsidian associated with Fayalite on mindat.org.
Pyroxene Group5 photos of Obsidian associated with Pyroxene Group on mindat.org.
Quartz2 photos of Obsidian associated with Quartz on mindat.org.
Opal-C2 photos of Obsidian associated with Opal-C on mindat.org.
Spessartine1 photo of Obsidian associated with Spessartine on mindat.org.
Rose Quartz1 photo of Obsidian associated with Rose Quartz on mindat.org.
Jasper1 photo of Obsidian associated with Jasper on mindat.org.
Tiger's Eye1 photo of Obsidian associated with Tiger's Eye on mindat.org.

References for ObsidianHide

Reference List:
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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.
http://members.peak.org/~obsidian/index.html (International Association for Obsidian Studies)

Internet Links for ObsidianHide

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