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Types of Obsidian
Obsidian volcanic rock forms when molten lava is quickly cooled. Lava that cools and forms obsidian at the surface is called extrusive; when it cools beneath the surface, it is called intrusive obsidian. Obsidian typically forms when lava comes into contact with water, either below or above the surface. Rapid cooling causes lava to solidify quickly, not giving crystals a chance to form; the resulting rock is shiny and slick, like glass, and is often referred to as volcanic glass. Obsidian is most typically black, but it can also be gray or a brown-and-black mix called mahogany; rarely, it is found in blue, red, orange or yellow hues. Black obsidian is the most common form in Nevada.
Nevada Obsidian Locations
Two types of obsidian are known to occur and are mined in Nevada, most commonly in the northern part of the state, near the Idaho border. This obsidian deposit is known as Brown's Bench. The southern tip of Nevada, in the areas around Devil's Peak, Roach Lake and Castle Mountain, also has a large obsidian deposit that is regularly mined. The northwestern corner of Nevada has many obsidian deposits, at locations including Hawks Valley, Badger Creek, Mosquito Lake and Coyote Spring.
Value and Use of Obsidian
The American Indians were the first Americans to exploit obsidian. Because it is easily fractured to create sharp edges, obsidian was used it to create knives and spear tips. It was used as a trade item, as well; because obsidian is not found east of the Mississippi River, it had great trade value for people living there. Obsidian's largest commercial value today lies in its use in the jewelry industry. It is polished and made into pendants for necklaces and beads and is used as a backing for opal pendants, in which its dark color provides a background that makes an opal's colors brighter and more apparent.