Topaz Crystals on Rhyolite

Topaz is a mineral that is formed as fluorine-rich vapors rise from cooling lava flows or intrusions of magma. This is how the crystals found at Topaz Mountain in Utah were formed.  The Thomas Range is world-famous for its topaz.  Most of the matrix rock is a white to gray-colored rhyolite that contains the lithophysae (Greek for "rock bubbles") which are spherulites that formed expanding gas cavities within the rhyolite.  Small gemmy topaz crystals were able to form in these cavities.

Topaz Valley, at the southern end of the Thomas Range, is perhaps the single most famous locality. While fine- quality, sherry-orange crystals to 5 cm or more in length occur at various localities, pale to medium pink crystals were first reported from the Thomas Range in 1934. Topaz occurs in a variety of colors. Colorado topaz is usually pale blue, while Utah topaz is a sherry brown or amber color. Utah topaz is light sensitive and, if left exposed to strong sunlight, the color may fade and the crystal can even become clear. Topaz crystals from Topaz Mountain tend to be small, but quite perfect. It is often said that the most beautiful little topaz crystals in the world are found here.

The Thomas Range and Topaz Mountain are located about 30 miles northwest of Delta, Utah. Most of the area is BLM land used for grazing cattle. It is a very arid region, very hot in the summer and very cold in the winter. This area is only for primitive camping, that means no water, firewood, or toilet facilities are available within at least a 20 miles radius. Small bushy trees may provide minimum relief from the hot summer sun. Primitive areas have lots of insects and local critters…if you come to collect here, come well prepared.