|Rough Opal From Opal Butte, Oregon|
While Australia produces over 97% of the worlds supply of opal today, Recent mining at Opal Butte in northeastern Oregon has produced a wide variety of large flawless opals.
The most common gem-quality varieties are hyalite and rainbow opal, but the less common play-of-color varieties contra luz, hydrophane, and crystal opal are economically more important. Opals are formed in rhyolite, basalt, sandstone, marl and rhyolite. Rhyolite geodes are a common source of opals. They are classified as mineraloids, meaning that they do not have the characteristics of crystals. It is a crystal like product of silicon dioxide which is deposited under somewhat low temperature and forms in fissures and cracks of rocks.
One way opals are formed is from water carrying a mineral called silica that seeps into volcanic lava. Lava has air bubbles that, as they cool, become receptacles for the liquid deposits. This is why Oregon is opal territory. From its position at the edge of the North American crustal plate, Oregon has played host to many volcanoes. If the conditions are right, the seeping silica forms opals within the volcanic air bubbles.
|The Oregon Opal with the Ocean inside|
Credit: Mckenna Praetorius
Oregon's Morrow County is the site of a large opal mining operation in an area called Opal Butte. Although these deposits were identified in the 1800s, they were not mined until 1988 when West Coast Gemstones, Inc. began work there. They have located and sold exquisite gems as large as 315 carats.
The Opal Butte opals are found in rhyolite geodes, also called thundereggs. Thundereggs can look like regular rocks on the outside but, broken open, can reveal agates or opals on the inside. Only about 10 percent of the total geodes mined at Opal Butte contain gem-quality opal, and only about 1 percent contain gem-quality opal with play of color. The remaining geodes contain agate, quartz crystals or common opal.
Opal Butte is not the only opal mining area in Oregon. The Last Chance Mine operates near La Pine in the Bend/Fort Rock District of the Deschutes National Forest, and a few others have mining claims in the area.
It appears that there are no other fee-dig opal mines in Oregon. Those looking for a fee dig mine near Oregon can try to Dig Your Own Unique Opals From Nevada.
|Oregon opal with visual effect of being underwater when held to light.obtained at Opal Butte Mine. Oregon, USA.|
Photo: Inna Gem