Wyoming Opal

Wyoming opal was long though to be non-existent. Then, small amounts of precious opal were discovered in central Wyoming. The search began and now Wyoming opal is quite a bit more common that previously thought, although it is still not really common.

There are two types of opal – common and precious. Precious opal has “fire” or iridescence and is the typical type of opal people imagine. Common opal has its own beauty. It does not have the iridescence of the precious opal, but it can be found in a wide range of colors and often is dendritic. It has a lovely sheen to it, despite its “plain” coloring.

In Wyoming, the opal is found in rocks that are 20-40 million years old. During this time, Wyoming, and much of the western interior, was vast grasslands and forests. A wide array of animals lived in this region and the Bandlands of South Dakota has made many of these mammals famous. Periodically, volcanic activity associated with Yellowstone would spew huge amounts of ash into the atmosphere and blanket the country (did you know that Yellowstone is the largest active volcano in the world? It erupts on a cycle of about every 200,000 years and produces an almost imaginable amount of ash). This ash is rich in silica and when it is buried later by more sediments as the grasslands and forests returned after the eruptions, the silica and fluids would permeate up into the overlying sediments. They would accumulate around and in fossils, especially wood. This can create petrified wood. If the silica has sufficient water with it, it produces opal. Occasionally, precious opalized limbs can be found in Wyoming. Most commonly, nodules of opal and agate are found with beautiful common opal.

The common opal shown here has a unique peach color with gray and white to it with black dendrites. Many of them have unusual patterns in the colors.