Topaz Mountain, a summit in western Utah’s Thomas Range, is renowned for its rich concentration of semiprecious minerals and long-standing appeal to rock collectors. Formed in volcanic rhyolite and water-laid rhyolitic tuff of Tertiary age, its topaz-bearing rock came from eruptions about six to seven million years ago, with crystals forming in cavities and later weathering onto slopes and arroyos. The mountain’s namesake topaz occurs as hard, transparent crystals, while the area is also noted for exceptionally rare red beryl and other minerals including opal, bixbyite, garnet, amethyst, pseudobrookite, and hematite. Public access has helped preserve its importance to both amateur and professional collectors.