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Obsidian

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13282000ObsidianAlso known as « obsidian glass », obsidian got its name from Roman general Obsius, who was the first to bring a sample of this stone from Ethiopia to Rome.ObsidianAlso known as « obsidian glass », obsidian got its name from Roman general Obsius, who was the...Zoom http://www.museum-lehavre.fr/sites/default/files/styles/exposition/public/objet/dsc_6840.jpg?itok=PNPHlIDTLe Havre Museum of Natural History - Photo C. Livonnen

Obsidian

 

  • Donor / collector : Serge Henry
  • Rock type : volcanic rock
  • Age : unknown
  • Origin : unknown
  • Dimensions : 5 cm x 6 cm

Also known as « obsidian glass », obsidian got its name from Roman general Obsius, who was the first to bring a sample of this stone from Ethiopia to Rome.

Obsidian is a hard and brittle extrusive igneous rock. There are several types of obsidian rocks which differ in their chemical compositions, but they all contain high levels of silicium.

Obsidian is dark in appearance (usually green, brown, grey, or black). Depending on its exposure to light, it sometimes includes silver or gold sheens, and even rainbow-like sheens when it contains magnetite or hematite nanoparticles.

Other varieties include the « snowflake obsidian », which contains radially clustered crystals (cristobalite) and the « mahogany obsidian », which are dark-brown to black with red sheens, because they contain traces of metal. « Apache tears » are rounded pebbles of obsidian which were formed by cooling down along sandy rivers.

This type of rock has been used since prehistoric times for the manufacture of cutting tools. It is also used for sculpture, especially in Mexico.

Origin : Aeolian Islands (Sicily, Italy), Antatolia (Turkey), Iceland, Java, Japan, USA, Mexico, Auvergne (France)

 

Composition : various silicates

Melting point : 1300°C

Hardness : 5 to 6

Density : 2 to 3

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