Rock crystal quartz, the most common gem variety of quartz crystal, is, like all quartz, formed from the two most abundant elements in the earth's crust: silicon and oxygen. For centuries early civilizations believed that these pinhead size to nearly a meter in diameter rock crystals were permanently frozen ice. Quartz's high thermo-conductivity, which makes it feel cool to the touch, may have added to this belief. Regardless of what early people may have believed, historical records show the use of rock crystal for decoration and jewelry for at least 4,000 years. Tools and weapons were made from rock crystal long before it was used for decoration and jewelry.
During the late 1980's and early 1990's, metaphysical uses and applications of rock crystal resulted in an increase in its production and processing. The metaphysical market used raw crystal in jewelry, person power and healing devices, and as charms. Additionally, spheres, sculls, pyramids, and other metaphysical objects were made from rock crystal. During the height of the trend, these uses accounted for 40% or more of the rock crystal consumed in the United States and also resulted in price increases for most of the crystals. Today, the metaphysical market has declined from its peak and appears to have stabilized at about 15% to 20% of total rock crystal consumption.
The market for rock crystal carvings, objects of art, and spheres is still strong. One piece of evidence of the demand for quality rock crystal for these types of uses is the level of sales of high quality quartz crystals from the National Defense Stockpile (NDS). During fiscal year 1994, sales of quartz crystals from the NDS totaled 313.1 metric tons valued at about $6.3 million, of this total, 96.8 metric tons valued at $3.21 million were sold during 6 days of the Tucson Gem and Mineral Show in February. During fiscal year 1993, NDS sold 176.8 metric tons of quartz valued at $1.64 million.
A gem dealer who purchased NDS quartz in Tucson shared the following information with the author: A 3,412 gram piece of quartz was purchased for about $120. The purchaser blocked out a totally flawless piece that was sent to a U.S. sphere cutting operation to be made into a flawless sphere. The sphere factory charged $48 to cut and polish a high-quality 84 millimeter, 844 gram sphere. The dealer sold the finished sphere for $1,200. This is only one dealers reported success in using NDS rock crystal and may not represent the outcome of any of the other NDS quartz sales.
Figure 8.--Rock crystal from Arkansas.
(Photo is courtesy of the author.)
Arkansas.--To many in the gemstone industry, Arkansas and rock crystal quartz are synonymous. Mount Ida, Fisher Mountain, Hot Springs, and Jessieville names mean quartz crystals to many people, but in fact, they are towns or places in the Arkansas quartz belt. Not only is Arkansas the major producer of gemstone and decorative rock crystal but it is the only producer of "lascas” the feed material used to make synthetic quartz.
The rock crystals are produced from quartz veins in sandstones and shales of the central part of the Ouachita Mountains. The quartz belt is about 240 kilometers long and 24 kilometers wide, extending southwest from near Little Rock all the way to northern Oklahoma. The crystals are beautifully formed with lustrous faces, many have water clear, colorless terminations. Commonly, they are milky in appearance because of inclusions. On large plates of crystals the crystals are often short and stubby, but in smaller crystals it is not unusual for them to have a length that are at least 6 times their diameter. Many of these slender points are used as “gem points” in making earrings and pendants.
Historically, the demand for crystals was from tourists, collectors, interior decorators, carvers, sphere makers, and certain industrial and military applications. However, in recent years the increased use of quartz crystals in the metaphysical field has greatly impacted the demand and price for Arkansas quartz. Another market for the crystals is as feed material to be irradiated to produce smoky quartz. Most smoky quartz from Arkansas is not natural, but is irradiated rock crystal. Although its not the only U.S. producer of rock crystals, Arkansas is by far the largest, its quartz crystal mining industry is measured in millions of dollars per year.
California.--Deposits in California are another source of significant amounts of quality rock crystal. For many years cobbles and round crystals have been found in streambeds in Amador and Calveras Counties. The best quality, largest, and most abundant crystals come from ancient stream channels in the Mokelumne Hill area of Calveras County. Over the years, various mines in the area have produced thousands of kilograms of rock crystal, with some of the individual crystals weighing as much as 275 kilograms and many of the crystals measuring more than 600 millimeters in length and 250 millimeters in diameter. The American Museum of Natural History has a 150 millimeter sphere cut from a Mokelumne Hill rock crystal. Additionally, the pegmatites of Hiriart Hill, San Diego County, have produced hundreds of kilograms of fine-quality rock crystal from which a number of 60 to 90 millimeter spheres have been cut.
New York.--Herkimer County, NY, is nearly as famous for its rock crystals as is Arkansas. The most productive area for "Herkimer diamonds", as the well-formed, mostly doubly-terminated rock crystals are known, is the rock outcrops and associated soils in a belt between the towns of Middleville and Herkimer, NY. The belt extends about 5 km south of Middleville. At least two other areas in the Middleville area also produce "Herkimers." Most mineral collectors feel their collection is incomplete without at least one Herkimer. The crystals are faceted, raw crystals are mounted to be used as pendants and earrings, and crystals are even bored to be strung as beads.
Currently, the crystals are not mined commercially but are collected by hobbyist and professional collectors. The crystals are found loose in the soil where they have weathered from the underlying rock or they are taken from cavities in freshly broken rock. The cavities maybe so small as to contain only a single 4 to 5 millimeter crystal or large enough to contain hundreds of crystals with some of the crystals over 100 millimeters in diameter. The smaller crystals, 4 to 12 millimeters, tend to be the best and some of the crystals contain inclusions of carbonaceous material and liquid- or gas-filled voids.
Others.--Arizona, Colorado, Idaho, Georgia, Montana, Nevada, North Carolina, South Carolina,
and Washington all produce some rock crystal each year. Most of the material ends up in mineral
collections, but some are cut into stones for jewelry and a small amount is used for carving. The
market for large, fine-quality rock crystals appears to be strong and every indication is that the
strong demand will continue, because of the increased demand for carvings.