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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. It is sometimes classified as a mineraloid. Pure obsidian is usually
dark in appearance, though the color varies depending on the presence of
impurities. Iron and magnesium typically give the obsidian a dark green to brown
to black color. Very few samples are nearly colorless. 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). 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. These bubbles
can produce interesting effects such as a golden sheen (sheen obsidian) or an
iridescent, rainbow-like sheen (rainbow obsidian).
Obsidian can be found in locations which have experienced rhyolitic eruptions.
It can be found in Argentina, Armenia, Azerbaijan, Canada, Chile, Greece, El
Salvador, Guatemala, Iceland, Italy, Japan, Kenya, Mexico, New Zealand, Peru,
Scotland and United States. Obsidian flows which may be hiked on 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. Yellowstone National Park has a mountainside containing obsidian
located between Mammoth Hot Springs and the Norris Geyser Basin, and deposits
can be found in many other western U.S. states including Arizona, Colorado, New
Mexico, Texas, Utah, Washington, Oregon and Idaho. Obsidian can also be found in
the eastern U.S. state of Virginia.
Obsidian was valued in Stone Age cultures because, like flint, it could be
fractured to produce sharp blades or arrowheads. Like all glass and some other
types of naturally occurring rocks, obsidian breaks with a characteristic
conchoidal fracture. It was also polished to create early mirrors. Modern
archaeologists have developed a relative dating system, obsidian hydration
dating, to calculate the age of obsidian artifacts.
Lithic analysis can be instrumental in understanding prehispanic groups in
Mesoamerica. 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. This is the
case in Yaxchilán, a Maya city where even warfare implications have been studied
linked with obsidian use and its debris. 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.
Pre-Columbian Mesoamericans' use of obsidian was extensive and sophisticated;
including carved and worked obsidian for tools and decorative objects.
Mesoamericans also made a type of sword with obsidian blades mounted in a wooden
body. 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.
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. Similar tracing techniques have allowed obsidian to be
identified in Greece also as coming from Melos, Nisyros or Yiali, islands in the
Aegean Sea. Obsidian cores and blades were traded great distances inland from
In Chile obsidian tools from Chaitén Volcano have been found
as far away as in Chan-Chan 400 km north of the volcano and also in sites 400 km
south of it.
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