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[13] [14] [15] Extrusive formation of obsidian may occur when felsic lava cools rapidly at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air. Intrusive formation of obsidian may occur when felsic lava cools along the edges of a dike. [16] [17]
Excessive water present during cooling and quenching of rhyolitic lava causes obsidian to hydrate (i.e., water entering the obsidian glass converts it to perlite). Where perlite is incompletely hydrated, fresh obsidian cores remain as pebbles of marekanite, or Apache tears; this origin has been occasionally described in the geologic literature ...
Obsidian from the Coso Volcanic Fields was heavily exploited by Native American Coso People to make knives, projectile points, and the like (Hughes 1998). The chief period of exploitation was between approximately 3000 and 1000 years ago, when people mined obsidian by constructing benches in hillsides and digging deep pits to access raw materials (Elston and Zeier 1984; Gilreath and Hildebrand ...
The lavas of different volcanoes, when cooled and hardened, differ much in their appearance and composition. If a rhyolite lava-stream cools quickly, it can quickly freeze into a black glassy substance called obsidian. When filled with bubbles of gas, the same lava may form the spongy appearing pumice. Allowed to cool slowly, it forms a light ...
Mono Paiutes gathered obsidian from the Mono–Inyo Craters to make sharp tools and arrow points. [38] Unworked obsidian was carried by the Mono Paiutes over passes in the Sierra Nevada to trade with other Native American groups. Chips of Mono–Inyo obsidian can still be found at many ancient mountain campsites. [39]
Flow banding in the obsidian dome. The central lava dome was erupted from degassed material and is made up of pumice and obsidian of the same composition. The difference between the two has to do with gas escaping as the magma cooled. The magma that created the dome had dissolved gas in it, like a bottle of seltzer water.
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Edziza obsidian found in coastal areas of southeast Alaska. Edziza obsidian is a naturally formed volcanic glass found at the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It occurs in at least four geological formations of the volcanic complex and was widely used by indigenous peoples during the pre-Columbian era.