Oregon State Rock
Thundereggs are round geological structures that formed inside gas bubbles in lava. This lava spread over the U.S. state of Oregon in the Eocene epoch, almost 60 million years ago. Groundwater moving through gas bubbles in the cooling lava deposited minerals, and eventually rocks were formed. Since thundereggs are a form of agate, they are composed mainly of silica. While most are two to six inches wide or a little larger than a baseball, thundereggs of over three feet (1 m) in diameter have been found.
The exterior surface of a thunderegg is an uninteresting, drab rind, often with a knobby appearance. It is the core that holds the prized material. When sawed open, the interior may be filled with crystals or may be an empty cavity. Many thundereggs reveal exquisite and colorful designs ranging from five-pointed stars to miniature landscapes.
Although similar to geodes, not all thundereggs are geodes. A geode has a hollow, which only some thundereggs have. Similarly, a geode is not a thunderegg if had a different geological formation.
A STATE SYMBOL
Oregon is one of the most well-known locations for thunderegg occurrences. The town of Nyssa, Oregon, was nicknamed the "Thunderegg Capital of the World" and is the location of an annual festival called Thunderegg Days. Oregon’s rockhounds voted on a state rock, and the state legislature designated thunderegg the official state rock of Oregon on March 5, 1965.
The name of this rock comes from a Native American legend of the Pacific Northwest. According to the legend, the "thunder spirits" who lived atop Mount Hood and Mount Washington in the Cascade Range threw these rocks at one another in anger during thunderstorms. It is believed these rocks are thunderbird eggs stolen by the gods.
FORMATION AND OCCURRENCE
Thundereggs formed in very soft, crumbly, volcanic ash beds. Solutions containing silica permeated the cinders until favorable points for chalcedony deposits were achieved. Aggregations of chalcedony were deposited. However, before the material could fully solidify, the center of the concretion split apart, possibly because of shrinkage, permitting the later introduction of additional materials. The resulting centers may be in the form of agate, jasper, calcite, different varieties of opal, or even carnelian or cinnabar. The centers may have quartz crystals, growths, or inclusions, or may be hollow.
Thundereggs can be collected all over Oregon, but the largest deposits are in the central and southeastern parts of the state. Oregon is probably the most important locality for thundereggs. They also occur in Doña Ana County, New Mexico in the United States, as well as in Germany, Poland, Romania, Turkey, Mexico, Argentina, Canada, Australia, France, and parts of Africa.
Due to the crystals and colorful agate they may contain, thundereggs are prized by amateur collectors and experienced lapidaries. Each rock has a different color, design, and pattern. They are used in a number of ways. One of the most common uses is to simply saw the thunderegg into two pieces, polish the sawed face of each half, and use it as a display or decorative piece; bookends are also made in this fashion. In addition, the thundereggs are sawed into slabs from which calibrated and freeform cabochons are cut. Thundereggs are used in pendants, pen stands, and decorative items. At least one firm in the United States is manufacturing gem spheres from thundereggs.
Chemical Formula: SiO2
Color: Occurs in an infinite range of colors. Most commonly white, purple, brown, and colorless. Many specimens are multicolored or banded.
|Author: World Trade Press|