One study found that obsidian produced narrower scars, fewer inflammatory cells, and less granulation tissue in a group of rats. When examined under an electron microscope an obsidian blade is still smooth and even. Even the sharpest metal knife has a jagged, irregular blade when viewed under a strong enough microscope. Obsidian is used in cardiac surgery, as well-crafted obsidian blades have a cutting edge many times sharper than high-quality steel surgical scalpels, with the edge of the blade being only about 3 nm wide. Modern archaeologists have developed a dating system Obsidian hydration dating to calculate the age of Obsidian artifacts. Obsidian was also used on Rapa Nui (Easter island) for edged tools such as Mataia and the pupils of the eyes of their Moai (statues). Obsidian cores and blades were traded great distances inland from the coast. Similar tracing techniques have allowed obsidian to be identified in Greece also as coming from either Melos, Nisyros or Yiali, islands in the Aegean Sea. 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. Native American people traded obsidian throughout North America. 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. Mesoamericans also made a type of sword with obsidian blades mounted in a wooden body. Pre-Columbian Mesoamericans' use of obsidian was extensive and sophisticated, including carved and worked obsidian for tools and decorative objects. 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 highly valued in certain Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads. Obsidian can also be found in the following countries: Armenia, Turkey, Italy, Mexico, Greece and Scotland. US states including Arizona, Colorado, Texas, Utah, and Idaho. Yellowstone National Park has a mountainside containing much obsidian located between Mammoth Hot Springs and the Norris Geyser Basin, and deposits can be found in many other western Among other places, large obsidan flows are found within the calderas of Newberry Volcano and Medicine Lake Volcano in the Cascade Range of western North America, and at Inyo Craters east of the Sierra Nevada in California. Obsidian can be found in many locations around the world which have experienced rhyolitic eruptions. These bubbles can produce interesting effects such as a golden sheen ( sheen obsidian) or a rainbow 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 green to 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 a 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 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.
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