In order to find obsidian in its natural state, you'd need to go to areas of geologically recent volcanic activity. In the United States, that means west of the Mississippi River. The International Association for Obsidian Studies refers to the Northwest Research Obsidian Studies Laboratory to list Utah sources of obsidian. These include the Black Rock Area, Browns Bench, Ferguson Wash, Marysvale, Modena, Phonolite Hill, Pumice Hole Mine, Pyramid Peak Vitrophyre, Topaz Mountain, White Mountain, Wildcat Hills and Wild Horse Canyon.
There is evidence that the obsidian quarries of Wildhorse Canyon, Utah, have been in use for thousands of years. The presence of three types of obsidian have been verified in the Wildhorse Canyon quarry. "True obsidian" is naturally occurring transparent obsidian (there are also clear obsidians with color; colorless obsidian does occur), but these pieces won't appear as large hunks and lumps, but in smaller deposits. True obsidian may have closely-spaced black bands. The pitchstone found at Wildhorse Canyon is much duller than most obsidian, which shines like glass. While still a black volcanic glass, it is dense and opaque. The "brown obsidian" at Wildhorse Canyon fits the description of Mahogany Obsidian. Impurities in obsidian change its appearance; for example, iron may cause it to appear reddish brown. Mahogany obsidian may range from an orangey to reddish brown, mottled with uneven splashes or streaks of black.
Also found in Utah are Apache Tears and Snowflake Obsidian. Apache Tears appear to be black pebbles -- they are obsidian, and therefore glass, rounded into smooth, small pebbles. Obsidian containing tiny crystals of cristobalite (a polymorph of silica and quartz) or feldspar reveals patterns of white flakes, leading to the name Snowflake Obsidian.
In contrast to the information provided by Utah rock hounds and hikers, however, are statements made by Mindat.org -- a database and reference website containing global mineralogical information -- which does not break out as many obsidian types. Mindat lists four types of obsidian and identifies only two types of obsidian as occurring in Utah: Mahogany Obsidian and Snowflake Obsidian.
Due to its rapid cooling, obsidian has very few mineral crystals; because it has no crystalline structure, it breaks on a curve (conchoidal fracture). The surfaces left by these breaks are extremely sharp, so many pre-industrial age peoples honed the sharp edges to form arrowheads, knives and even mirrors. Presently, obsidian is commonly used for jewelry, decorative items and fine surgical blades.
