Oregon Gemstone Mining
Oregon is a leading state for gemstone production with sunstone, thundereggs, opal and more.
Author: Hobart M. King, Ph.D., GIA Graduate Gemologist
A Diversity of Gems
Oregon is one of the nation's leading states for the production of gemstones. These gemstones are mostly a result of the state's long volcanic history. Oregon's famous sunstone is produced from basalt flows, thundereggs are formed in rhyolite, and the silica that produced much of Oregon's opal, agate, and jasper was dissolved from volcanic rocks by hot groundwater.
In the sections below we feature Oregon sunstone, thundereggs, opal, and the chalcedony gems of agate and jasper. Oregon has many other gems, which include obsidian, garnet, jade, steatite, wonderstone, and many varieties of petrified wood.
Table of Contents
Opal: Precious, Fire, and Common
Agates, Jasper, and Wood
Oregon produces some of the best gem-quality feldspar in the world. The name "Oregon Sunstone" is used for gem-quality feldspars from Oregon, with and without aventurescence. They can be found in colors that range from clear through yellow, orange, pink, red, green, and blue. Multiple colors are often found in the same crystal, making bicolor and tricolor stones possible.
Some specimens of Oregon Sunstone contain microscopic copper platelets suspended throughout the material. These platelets are often in alignment within the stone, and light entering the stone at the proper angle will simultaneously reflect from them. When these stones are played in the light, bright copper-colored flashes are produced as the stone passes through the angle of reflection. Flashes can also be observed by moving the light source or changing the angle of observation. This interaction with light produces the phenomenon known as aventurescence.
Sunstone is cut into faceted stones and cabochons. Material with platelets is usually cut to produce flashes of light when the stone is viewed in the face-up orientation. To do this, the copper platelets should be parallel to the top and bottom of the stone. Quality material cut by a skilled artisan is so attractive that the State Legislature named Oregon Sunstone the state's official gemstone.
The sunstones are found as phenocrysts in a small number of basalt flows. This makes production a labor-intensive job. They can be screened by hand from soils which have developed above the basalts. Hard-rock mining of the basalt is sometimes done, but it is less successful because the feldspar cleaves easily and breaks during extraction.
The most popular rock in Oregon is said to be the "thunderegg." Thundereggs are "nodules" or "geodes" that form when agate, chalcedony, or opal precipitate within the cavities of rhyolite, welded tuff, or perlite. Thundereggs can be ugly on the outside; however, when they are cut or broken open, a treasure of colorful gem material and crystals is often revealed. Thundereggs range in size from less than one inch to over three feet in diameter.
The mystery of breaking or sawing thundereggs to see what is inside is a large part of what makes them so popular. They frequently contain layered or fortification patterns of colorful agate, sometimes with a drusy quartz-lined inner cavity. Other specimens contain clear to milky or mossy chalcedony.
Oregon has one of the best places on this planet for finding obsidian, a volcanic glass and a mineraloid that is usually black in color. The location is Glass Butte and Little Glass Butte and surrounding areas in central Oregon. There, about 4.9 million years ago, volcanic domes and rhyolite flows produced some of the most spectacular obsidian varieties that you will find anywhere (see photo).
If you go there you will certainly find the typical black obsidian. You also have a chance to find exotic varieties like gold sheen (an aventurescent obsidian), rainbow (an iridescent obsidian), mahogany (a black and brown swirled obsidian), pumpkin (an orangey variety), and double flow (a black and orangey material swirled together). For collecting details see the Deschutes National Forest website.
Opal: Precious, Fire, and Common
A number of different types of opal are found in Oregon. An area known as Opal Butte in Morrow County has produced hyalite, hydrophane, crystal, contra luz, fire, common, dendritic, and other varieties of opal. Although some of the opal found there is unstable during cutting, a number of great gemstones are still produced.
A small fraction of Oregon thundereggs are filled with opal, and a smaller fraction of those contain gem-quality material with play-of-color. Some contain a blue opal known as Owyhee Blue that ranges from a blue gray to a brilliant sky blue. Some contain common opal with beautiful scenes and patterns like the cabochon pictured. The hope of finding opal or colorful chalcedony is what drives much of the thunderegg popularity.
Agates, Jasper, and Wood
The volcanic history of Oregon has produced a wide variety of agates and jaspers. Widely known Oregon agates include: Graveyard Point, Priday Ranch, Eagle Rock, Holley Blue, Richardson Ranch and Polka Dot. Widely known Oregon jaspers include: Biggs, Bat Cave, Blue Mountain, Morrisonite, Chicken Track, Deschutes, Spiderman, and Sucker Creek.
A popular activity along Pacific coast beaches is hunting agates and jaspers that have been tumbled in the surf. Some of the beaches have names such as "Agate Beach" that reveal what you might find there. Before you start hunting agates, be sure that collecting is allowed. Many beaches are private or government property where removing anything is forbidden.
Rivers draining the volcanic landscape of the western side of the Cascade Mountain Range carry large numbers of agate nodules of various sizes and dump them into the ocean. Then waves pick them up and roll them around in the surf. This action rounds the agates and gives many of them a natural matte finish.
A great time to look for agates is after a large storm, when streams have dumped more agates into the ocean and waves have disturbed the sand to expose agates that have not been found by people. Agates found on Oregon beaches are often nicely rounded and can easily be used to produce nice polished stones in a rock tumbler.
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