Obsidian

This article is about a type of volcanic glass. For other uses see obsidian (disambiguation).

Obsidian is a type of naturally-occurring glass formed as an extrusive igneous rock. It is produced when rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid. Because of the lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as projectile points, and its modern use as surgical scalpel blades.

Origin and properties

  Obsidian is perlite. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis.

Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. 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 a rainbow sheen (rainbow obsidian).    

Occurrence

Obsidian can be found in many locations around the world which have experienced rhyolitic eruptions. 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. 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 US states including Arizona, Colorado, Texas, Utah, and Idaho. Obsidian can also be found in the following countries: Armenia, Turkey, Italy, Mexico, Greece and Scotland.

Historical use

  Obsidian was highly valued in certain Stone Age cultures because, like conchoidal fracture. It was also polished to create early mirrors.

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 North America. 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 either Melos, Nisyros or Yiali, islands in the Aegean Sea. Obsidian cores and blades were traded great distances inland from the coast.

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).

Modern archaeologists have developed a dating system Obsidian hydration dating to calculate the age of Obsidian artifacts.

Current use

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 ^[2]. Even the sharpest metal knife has a jagged, irregular blade when viewed under a strong enough microscope. When examined under an electron microscope an obsidian blade is still smooth and even. One study found that obsidian produced narrower scars, fewer inflammatory cells, and less granulation tissue in a group of rats.^[3]

Obsidian is also used for ornamental purposes and as a perlite matrix.

See also

• Volcanic glass
• basaltic composition
• Obsidian use in Mesoamerica
• Flint knapping
• Obsidian hydration dating

References

1. ^ Perlite - Mineral Deposit Profiles, B.C. Geological Survey. Retrieved on 2007-11-20.
2. ^ Buck B.A. 1982. Ancient technology in contemporary surgery. The Western Journal of Medicine, 136, 265-269
3. ^ A comparison of obsidian and surgical steel scalpe...[Plast Reconstr Surg. 1993 - PubMed Result]. Retrieved on 2007-11-20.