Chalcedony is a catch all term that includes many well known varieties of cryptocrystalline quartz gemstones. They are found in all 50 States, in many colors and color combinations, and in sedimentary, igneous, and metamorphic rocks. Chalcedony includes carnelian, sard, plasma, prase, bloodstone, onyx, sardonyx, chrysoprase, thundereggs, agate, flint, chert, jasper, petrified wood, and petrified dinosaur bone just to name a few of the better known varieties.
Because of its abundance, durability, and beauty, chalcedony was, except for sticks, animal skins, bones, plain rocks, and possibly obsidian, the earliest raw material used by humankind. The earliest recorded use of chalcedony was for projectile points, knives, tools, and containers such as cups and bowls. Early man made weapons and tools from many varieties of chalcedony including agate, agatized coral, flint, jasper, and petrified wood.
The move from using certain items as weapons and tools, to using the same items for ceremonial and personal adornment is very easily made. It was only natural for early man to use his finest looking knife for special occasions or to attach a special lance point or arrowhead to his tunic. In fact, agate and petrified wood may have simply been elevated to gems from common and functional weapons or tools.
All 50 States produce some variety of chalcedony, but the material from some States is better known than that from others.
Figure 1 -- "Mojave Blue" agate from California.
(Photo is courtesy of Mr. Bill Nicks.)
Alaska -- The State has several varieties of chalcedony found at different locations, including agates, jaspers, and petrified wood. Various types of agates can be found in gravel pits and gravels of stream and river beds at several locations in the Chicken Creek area near the border with the Yukon Territory.
Agates, jasper, and petrified wood can be found on many beaches, including those on the islands of Adak, Admiralty, Attu, Kuiu, Kupreanof, Nelson, Popof, Tanaga, Unalaska, and Zarembo. These same materials can be found in the gravels or in many of the streams and rivers of the State. Other well known sources are the outlet of Becharof Lake, Little Nelchina River, and Caribou Creek.
Arizona -- Arizona is well known for its petrified wood because of the Petrified Forest National Park, and petrified wood ranks third in value of commercially produced gemstones. It is generally accepted that the Park contains the most colorful examples of silicified logs in the world.
Petrified wood occurs in every county in the State, but the commercial production is essentially from privately owned lands in Navajo and Apache Counties near the Petrified Forest. Federal regulations restrict collecting petrified wood on public lands to 250 pounds plus one piece per person per year, none of which is supposed to be sold commercially. The regulation essentially eliminates production from federal lands. Pieces as small as 1/4-inch to sections of logs 5 feet in diameter are recovered from the surface of the ground or with minimum excavations for use in the lapidary trade.
Arizona petrified wood has the broadest range of applications of any gem material produced in the State. The material is suitable for tumble polishing for use in baroque jewelry or for cutting into cabochons for jewelry and display. Freeform and calibrated slabs are polished for pen and pencil set bases and bases of other items, and polished slabs are used for clock faces. Additionally, large blocks, limb sections, and geometric shapes are used as bookends and decorator pieces. Objects of art, principally carvings, are produced, and furniture such as coffee and end tables are made from the petrified wood.
Arizona is the only State currently to have commercial production of fire agate. Fire agate is a form of chalcedony which contains inclusion of iron oxides that result in a play of colors much like that of precious opal. Eleven operations in Arizona report either commercial production of fire agate or dig-for-fee production. The material is produced in Graham, Greenlee, Maricopa, Mohave, and Yuma Counties.
Fire agate is cut into freeform and calibrated cabochons for use in the manufacture of silver and gold jewelry. The material is popular in the southwest and with hobbyist lapidaries throughout the United States. Fire agate also has been used and is currently used in Indian style jewelry.
California -- California's "Mojave Blue" agate has gained a great deal of attention in the past several years. This pastel blue or blue-gray agate cuts into attractive cabochons for jewelry and, in the hands of an expert carver, makes outstanding carvings.
Colorado and Utah -- These States have deposits of fine quality jasper, agate, petrified wood, and agatized dinosaur bone. These deposits are found over a large area of both States and on both sides of the continental divide in Colorado.
Florida--The famous silicified coral, first found in the Tampa Bay area around 1825 is the only gemstone of note from the State. Since its discovery in Tampa Bay, the agatized coral also has been found at Tarpon Springs, south of New Port Richey, near the town of Kathleen, and along the banks of the Suwanee River in Hamilton, Columbia, and Suwanee Counties. The material is found in two forms, as geodes, which represent partial replacement of coral, and as solid pieces which represent total replacement.
The coral is replaced by a waxy, translucent, botryoidal, varicolored chalcedony. The geodes are most often used as mineral specimens, but cabochon and tumbled gems can be made from the thin geode lining. The total replaced coral can be cut into attractive cabochons. The material can be blue, red, brown, amber, white, black, or a combination of these colors.
Idaho -- Jasper mining was beginning to make a comeback in the State, particularly with the operation of the Willow Creek jasper mine when in 1992, the untimely death of one of the partners mining the property, resulted in jasper mining reverting to hobbyist and professional collectors. Production of the various jaspers should be adequate to meet demand for the foreseeable future.
Montana -- Montana moss Agate is the grayish-white to gray translucent chalcedony containing dendrites. The black, brown, or red tree-like or scenic dendritic growths are actually included minerals of manganese and iron. Most of the moss agate is found as water worn cobbles in the Yellowstone River or its drainages between Billings and Sidney. The material can be collected in Yellowstone, Treasure, Rosebud, Custer, Prairie, Dawson, and Richland Counties. The agate has long been a favorite of hobbyist and professional cutters because of the beautiful and highly variable patterns, the durability, and ease in cutting and polishing.
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 volcanos, 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.
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 Custer, 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 Custer 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.
U.S. Department of the Interior
U.S. Geological Survey
988 National Center
Reston, VA 20192 USA
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Last modification: 11-Jan-2013@16:57