Pre-Columbian Mesoamericans' use of obsidian was extensive and sophisticated including carved and worked obsidian for tools and decorative objects. Another example is the archeological recovery at coastal Chumash sites in California indicating considerable trade with the distant site of Casa Diablo, California in the Sierra Nevada Mountains. This is the case in Yaxchilán, a Maya city where even warfare implications have been studied linked with obsidian use and its debris. A careful analysis of obsidian in a culture or place can be of considerable use to reconstruct commerce, production, distribution and thereby understand economic, social and political aspects of a civilization. Lithic analysis can be instrumental in understanding prehispanic groups in Mesoamerica. On display at the Museo de Arte Popular, Mexico City. Obsidian worked into plates and other wares by Victor Lopez Pelcastre of Nopalillo, Epazoyucan, Hidalgo. In the east of the Mediterranean the material was used to make tools, mirrors and decorative objects. Obsidian was also used in ritual circumcisions because of its deftness and sharpness. Īncient Egyptians used obsidian imported from the eastern Mediterranean and southern Red Sea regions. In Ubaid in the 5th millennium BC, blades were manufactured from obsidian mined in what is now Turkey. Modern archaeologists have developed a relative dating system, obsidian hydration dating, to calculate the age of obsidian artifacts. It was also polished to create early mirrors. Like all glass and some other types of naturally occurring rocks, obsidian breaks with a characteristic conchoidal fracture. Obsidian was valued in Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads. The first archaeological evidence (L.Leakey 1948) known of usage were made from within Kariandusi dated 700,000 BC (Merreck & Brown). These bubbles can produce interesting effects such as a golden sheen ( sheen obsidian) or an iridescent, rainbow-like sheen ( rainbow obsidian). It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. In some stones, the inclusion of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern ( snowflake obsidian). Iron and magnesium typically give the obsidian a dark brown to black color. Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Obsidian has low water content when fresh, typically less than 1% water by weight, but becomes progressively hydrated when exposed to groundwater, forming perlite. This breakdown of obsidian is accelerated by the presence of water. Because obsidian is metastable at the Earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. Crystalline rocks with obsidian's composition include granite and rhyolite. Obsidian consists mainly of SiO 2 ( silicon dioxide), usually 70% or more. Though obsidian is usually dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. It is sometimes classified as a mineraloid. Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline in addition, its composition is too complex to comprise a single mineral. The translation into english of Natural History written by the elder Pliny of Greece shows a few sentences subjected to volcanic glass called Obsian, so named from its resemblance to a stone found in Ethiopia by Obsius ( obsiānus lapis). among the various forms of glass we may reckon Obsian glass, a substance very similar to the stone found by Obsius in Aethiopia. Obsidian is hard and brittle it therefore fractures with very sharp edges, which had been used in the past in cutting and piercing tools, and are still used as surgical scalpel blades. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. For other uses, see Obsidian (disambiguation).
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