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Similar tracing techniques have allowed obsidian to be identified in Greece also as coming from Milos, Nisyros or Gyali, islands in the Aegean Sea.Obsidian cores and blades were traded great distances inland from the coast.Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline; in addition, its composition is too variable to be classified as a mineral. 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.This breakdown of obsidian is accelerated by the presence of water.Called a macuahuitl, the weapon was capable of inflicting terrible injuries, combining the sharp cutting edge of an obsidian blade with the ragged cut of a serrated weapon.The pole arm version of this weapon was called tepoztopilli.Iron and other transition elements may give the obsidian a dark brown to black color. 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).
Eight obsidian artifacts dating to the Chalcolithic Age found at this site were traced to obsidian sources in Anatolia.Native American people traded obsidian throughout the Americas.Each volcano and in some cases each volcanic eruption produces a distinguishable type of obsidian, making it possible for archaeologists to trace the origins of a particular artifact.Having a low water content when newly formed, typically less than 1% water by weight, obsidian becomes progressively hydrated when exposed to groundwater, forming perlite.Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities.