It took fourteen million years for Mother Nature to make a Virgin Valley opal.
It was well worth the wait.
The most spectacular black opals in the world come from the Royal Peacock mines in Virgin Valley, Nevada. Virgin Valley opals are found in layers of clay that were formed when volcanic ash filled an ancient lake millions of years ago. The surrounding forests were also choked with the ash. The lake had twigs and limbs and rotting wood collected in its coves. The buried wood decayed and left lifelike cavities as mementos of their presence.
Heat and pressure formed a silica gel that percolated through the ash and filled the cavities. It gradually hardened into opal. In a small percentage of the opals the cells aligned to create opals with a fiery soul -- precious black opals -- the most beautiful gemstones in the known universe.
Of course, not all Virgin Valley opals are "black." We also produce moss opal, lemon opal, crystal opal, and white opal. Additionally, we are the only known source for fluorescent opal, which fluoresces green when illuminated with black light.
Virgin Valley opals are predominately limb casts embedded in clay beds. Most limbs come from an ancient tree species called Cryptomeria, a relative of the Sequoia.
Modern day Cryptomeria are native only to Japan. A few opalized limbs have also been identified as coming from Fir, Pine, Oak, Chestnut, Maple, and Elm, as well as Ginkgo, a mostly extinct genus of trees found today only in Asia.
Virgin Valley opals are usually found in pockets. When you find one there are usually others nearby. This reinforces the current theory that most of the limbs were floating in an ancient lake, and crowded together in small coves and back eddies.
Opalized bones and teeth of vertebrate animals have also been found, including teeth from the now-extinct three-toed horse (Miohippus).
Opalized Miohippus (three-toed horse) Teeth
Other finds include opalized branches, bark, roots, pine cones, and seeds.
Another unusual discovery was several fossilized skeletons of prehistoric pigs. The bones are from a type of pig previously not found west of the Rockies.