Chalcedony (part3)

All 50 States produce some variety of chalcedony, but the material from some States is better known than that from others

New Mexico -- Varieties of agate, jasper, chert, or petrified wood are found in 15 of New Mexico's 32 counties. An area of about 100 hectares near Deming, New Mexico Rockhound State Park, is set aside for the non-commercial collecting of agate, jasper, and petrified wood.

Oregon -- The State is known for the production of various picture and scenic jaspers, agates, thundereggs, and petrified wood. Graveyard Point, Priday, and Polka Dot are names that are familiar to most agate collectors rockhounds, and many lapidaries. These are also names that are uniquely associated with Oregon and with beautiful agates. The same is true for the relationship between the names Biggs, Deschutes, and Sucker Creek and high quality picture or scenic jasper.

Oregon's State rock, the "thunderegg," may be the best known gem material from Oregon. Thundereggs were not, as believed by some people, ejected from volcanoes, but formed in very soft and friable volcanic ash beds. Solutions containing silica permeated the cinders until favorable points for chalcedony deposition were achieved. Aggregations of chalcedony were deposited, but 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 star-shaped centers of chalcedony may be in the form of agate, jasper, or in some cases different varieties of opal.

Thundereggs 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. Also, the thundereggs are sawed into slabs from which calibrated and freeform cabochons are cut. Additionally, at least one firm in the United States is manufacturing gem spheres from thundereggs.

"Mojave Blue" agate from California.
(Photo is courtesy of Mr. Bill Nicks.)

South Dakota -- The State's best known chalcedony is its colorful and beautiful Fairburn agates. Named after a community near a very prolific agate deposit in Custer County, these brightly colored banded agates are similar to Lake Superior agates found in Michigan and Dryhead agates from Montana. The color patterns are alternating bands with one of the bands always white. The colors that alternate with white include yellowish-brown, dark red, salmon pink, black, yellow, grayish-blue, and milky-pink.

The agate nodules range in size from about 20 millimeters in diameter to some that weigh as much as 20 kilograms. The nodules are recovered from the weathering of the Chadron formation in an elongated belt covering parts of Cluster, Pennington, and Shannon Counties, with the community of Fairburn at about the center of the belt. Nodules similar to the Fairburn nodules weather out of a limestone formation in an area that includes parts of Cluster and Fall River Counties.

Other varieties of agate are found in the State. Moss agate, much like the famous Montana moss agate, can be found in river gravels of the Little Missouri River system in Harding County. A wide variety of agate can be found in the gravel pits in the entire eastern part of the State.

Tennessee -- Agates can be collected from many different locations and geological formations across the State. The material includes golden tone agate from Hawkins Co., agatized oolites from Greene Co., carnelian, blue, ivory, pink, finely banded, dendritic, moss, iris and Fairburn style agate from Bedford Co., and Lake Superior type agate and agatized corals and sponges from Shelby Co. All of the material is suitable for cutting and takes a good polish.

Texas -- Some of the best agate, jasper, chert, and petrified wood (particularly petrified palm wood) found in the nation comes from Texas. Blue banded, moss, and red and black plume agates are found near Alpine in Brewster County. Similar agates are found in Jeff Davis, Hidalgo, Hudspeth, Presidio, Reeves, San Patrico, and Starr Counties. Petrified wood can be found in Amarillo, Bastrop, Brazo, Comal, Duval, Fayette, Gonzales, Lavaca, and Uvalde Counties, with fine-quality palm wood coming from Live Oak and Webb Counties. Good-quality chert can be found in limestone formations in McCulloch, Moore, and San Saba Counties. The material from Moore County also is called Alibates flint and was used by prehistoric and modern-day Indians to make weapons and tools. The quarry from which the Indians obtained their flint is now Alibates State Park.

Washington -- Washington' s petrified woods are some of the finest in the nation. The woods not only represent a broad range of colors and patterns, but also represent a wide range of identifiable species. Species identified include redwood, oak (more than 10 varieties), cypress, elm, maple, willow, cedar, poplar, chestnut, alder, birch, persimmon, laurel, and ginkgo. The preserved woods have been used to make cabochons, table tops, pen bases, and other objects of art.

Deposits in the State also furnish a selection of agates that include moss, blue, and carnelian. The blue agate from Kittitas County, known as Ellensburg Blue, is highly prized by local lapidaries.

Wyoming -- Wyoming's claim to fame is its fine-quality agates and petrified wood. Deposits across the State supply a variety of seam, moss, banded, fortification, and turritella agates. Colorful and attractive specimens of petrified wood can be found in many areas in the State.

Others -- This is by no means a complete summary of chalcedony production in the United States. Flint from Flint Ridge, OH, and Lake Superior Agate from the Great Lakes were not discussed, nor was many other agates or jaspers from individuals favorite collecting locations. But in the space available, the better known or commercial producing locations were mentioned.

In 1993, U S. production of gem chalcedony was valued at about $1.9 million, according to the USBM. The production and use of U.S. chalcedony as a gemstone will continue to grow because the material is beautiful, abundant, durable, reasonably priced, and the variability is nearly unlimited.

Article source: U.S.G. S.