Idaho. In Idaho, opal is the second largest contributor to the total value of gem material produced. The varieties produced include precious (white and pink), yellow, blue, pink, and common. The Spencer opal mine, the largest privately owned gemstone producer in the State, is the major producer of opal. At Spencer the precious opal occurs as one or more thin layers within common opal partially filling gas cavities within a rhyolite-obsidian flow. About 10% of the material is thick enough to cut into solid gems; the remainder is fashioned into doublets and triplets. The Spencer Mine is the source of pink common opal and pink precious opal.

Louisiana. The reported precious opal from Louisiana is a sandstone/quartzite with precious opal cement and matrix. It has blue or purple play of color. The material could be cut into cabochons for jewelry and other items of interest. To date, most of the material has been cut into large (over 2-inches in diameter) gemstone spheres.

Nevada. Nevada is known for precious opal from Virgin Valley. The first discovery of precious opal in the Virgin Valley area was in 1905 or 1906. Since then a significant quantity of the highly prized opal has been recovered. Virgin Valley opal is comparable to any in the world for its vivid play of color and in terms of the size of material available. Individual pieces weighing over 3 kilograms have been recovered from the Virgin Valley deposits. In 1993, miners found a 100-kilogram opalized log containing precious opal. The material varies in body color from deep pure black to brown to yellowish-white to white to colorless. The play of color includes all colors common to precious opal, red, blue, green, yellow, orange, etc. The opal occurs primarily as replacement of wood, or sometimes, as replacement of conifer cones. Some opal does occur as nodules filling void spaces in clay. The wood replacement is so complete, that generally the wood grain and banding are no longer visible. The exception to this would be that often the exterior wood texture is still present as a brown or black rind.

Contra luz opal from Oregon.
(Photo is courtesy of Kevin Lane Smith.)

Oregon. During 1988, West Coast Gemstones, Inc., began mining and marketing a variety of very fine-quality opals from Opal Butte in Morrow County, OR. The varieties produced includes hyalite, rainbow, contra luz, hydrophane, crystal, fire, blue, and dendritic. Exquisite stones as large as 315 carats have been cut from contra luz rough from this deposit. The deposit at Opal Butte has been known since the late 1800's. It was of interest only to hobbyists until recently because people believed most of the opal was unstable. Stability can be a problem with the opal, crazing can occur when stresses are created from shrinkage due to water loss. West Coast has developed methods of drying the opal that greatly reduce crazing. Even with the drying procedures, the stability varies from 20% to 90% depending upon the variety. The opals are found in rhyolite geodes (thundereggs) in a perlite that has altered to a pastel colored clay. The geodes that contain gem-quality opal are only about 10% of the total geodes mined and only about 1% of the geodes contain gem-quality opal with play of color. The remaining geodes contain agate, quartz crystals, or common opal. The geodes vary greatly in size, from a few centimeters in diameter to over a meter. The deposit continues to produce a supply of very fine quality opal for cutting and carving. Currently, a company has launched an American gemstone jewelry line based on the Opal Butte's opal. Plans are to operate the mine for at least the next 5 years.