Obsidian
The obsidian is a Volcanic rock vitreous and rich in Silice.
Of color gray, green dark, red or black, it is resulting from a Lave which cooled so quickly that it practically did not crystallize. That can arrive at the time of volcanic eruptions under navy.
Its name would come from Obsius , a character of the ancient Rome which announced in first the presence of this rock in Ethiopia.
Physical properties
The obsidian is transparent with translucent and present a vitreous texture and glare. Its break is very clearly Conchoïdal E, its high hardness Mohs: 5 to 5,5 (it raye glass).Recrystallization
Glass of the obsidian can recristallize what gives Sphérolithe S of Feldspath. That gives obsidians “snowflake”.
Layers
The obsidian is formed from lava flow very thick and rich in silica. The cooling of casting was very fast and the magmatic liquid was transformed into glass.
Common rock not very, the obsidian is in abundance:
- on the islands Lipari, one of the Wind Islands (Italy), in Sardinia (Arci Goes up)
- in the surroundings of Landmannalaugar (Iceland),
- like with the Mexico, Peru, the United States, Japan and Arménie…
Prehistoric use
The obsidian was used for the manufacture of edge for the weapons and the tools during the Préhistoire, in particular in America précolombienne. The rolled rollers are used with manufacture as jewels.There also exists of many traces of use of the obsidian in the south of Europe to the Neolithic , where and a transport form of trade of the stone was installation since the layers of the volcanos of current Italy. Obsidian tools were thus found at the time of Fouille S archaeological, in particular in the south of France. With the advent of the Neolithic era in the Western Mediterranean, 8000 years ago, of the networks of exchanges are set up between the various communities agropastorales. A recent study relating to the prehistoric obsidian makes it possible to raise a veil on the way in which were organized certain of these exchanges with long distances, between the Mediterranean islands and shores: this trade was partly with the hands of specialized craftsmen who moved by sea route and distributed the product of their craft industry to the visited communities. The archeological sites attest working of the Nucléus around the layers (mainly Lipari and Monte Arci in Sardinia), then detachment of blades and plates in the villages " consommateurs" .
See too
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