Topaz Mountain, Mountain peak in Juab County, United States.

Topaz Mountain is a 2,142-metre summit in the Thomas Range of Juab County, Utah, about 36 miles northwest of Delta. Its slopes expose rhyolite, a volcanic rock formed 6–7 million years ago, in which amber topaz crystals occur in cavities and loose on the ground.

Red beryl in topaz-bearing rhyolite was known on Topaz Mountain since 1905. In 1959, beryllium deposits in the form of bertrandite were found overlying the rhyolitic tuff on nearby Spor Mountain. The topaz itself formed in cavities of rhyolite from eruptions during the Tertiary Period, six to seven million years ago.

Topaz Mountain lies on public land managed by the Bureau of Land Management, where collecting rocks and minerals is permitted, so amateur and professional rockhounds work the slopes and arroyos with picks. Red beryl, known here since 1905, is the rarest find: roughly one crystal exists for every 150,000 diamonds, and faceted stones can reach $10,000 per carat.

The summit lies on Bureau of Land Management land about 36 miles northwest of Delta, reached by graded dirt roads; a high-clearance vehicle is advisable. Rock and mineral collecting is permitted, but red beryl may sit on private claims and must not be dug or removed. Bring water, sun protection, containers and gloves, and watch for snakes.

The topaz crystals found here naturally shift from amber to clear when exposed to extended sunlight, a gradual change that happens over time. This light-triggered transformation is one reason why collectors find this location particularly noteworthy.