GENERAL GEOLOGY

Detailed explanation-1: -However, the best quality obsidian often forms below the ground surface around volcanic vents. Silica-rich magma squeezes into rock fractures to form layers and lenses of obsidian that are relatively free of dirt, ash and other impurities.

Detailed explanation-2: -Most obsidian is associated with volcanic rocks and forms the upper portion of rhyolitic lava flows. It occurs less abundantly as thin edges of dikes and sills.

Detailed explanation-3: -Obsidian is found near volcanoes in locations which have undergone rhyolitic eruptions.

Detailed explanation-4: -Obsidian is a naturally occurring volcanic glass. It is formed during the eruption of felsic lavas, which are distinguished by having high concentrations of the chemical element silica. Because of their high silica content, felsic lavas do not behave like the mafic, or silica-poor, lavas we see on the island of Hawaii.