Obsidian Walhalla This is an 180,000 year old rhyolite flow at Obsidian Cliff in Yellowstone Nationa

Obsidian WalhallaThis is an 180,000 year old rhyolite flow at Obsidian Cliff in Yellowstone National Park. Rhyolite is a type of lava that is very sticky and thick and also has the tendency to contain obsidian. Although it is not very apparent when you look at these cliffs, they do harbor a huge amount of obsidian. Apparently the black, shiny volcanic glass is visible on the cliffs around sunset. Obsidian was used as instrument in surgeries until last century due to its extreme sharpness. When lava cools so quickly that crystals do not have time to come into being, obsidian forms. In this case lava might have interacted with ice of a glacier causing it to rapidly cool. The characteristic columns of the cliffs are also a result of rhyolite rapidly cooling. The obsidian is most abundant at the base of the cliffs.Around 11,000 year ago the Native inhabitants of the region of Yellowstone realized the potential of the volcanic glass. The area soon became a quarry for tools, weapons and ceremonial objects. These objects were traded as far as Mexico! Obsidian has a very specific composition, making it possible for archaeologists to reveal their origin even from a very smallest amount of it (a flake). This is done by using trace-and bulk – element geochemistry. Nowadays it is strictly forbidden to collect obsidian at the cliffs.-OW-Image: USGS. The rhyolite columns at Obsidian cliffs.References:http://pubs.usgs.gov/fs/2005/3024/http://www.nps.gov/yell/planyourvisit/upload/250Obsidian2013-3.pdf -- source link

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