Excerpts from
a college
classroom
lecture
by J. Michael H.
Index to Quartz
Digging
Cleaning
Worth
Fee Pay Mines
Types
Forms
Inclusions
Geology
Mineralogy
Metaphysics
Synthetic
Gemstones
Handedness
Experiments
Photos from readers
Chapter 1 Page 13
Colorless Quartz, also known as rock crystal, Part 1
CRYSTAL IS A TERM that began with the ancient Greeks to describe the colorless variety of the mineral quartz. They thought that water from deep in caves had frozen so solid that it would not thaw. The Medieval Japanese thought that rock crystal was ice or snow that was frozen hard. These beliefs probably originated from the fact that during this time much rock crystal was collected from veins that filled rock clefts in the mountains, where glaciers and permanent ice is seen. In the absence of modern science, we might think the same! In 1669, the great Danish physician, theologian, and geologist, Steno, made a startling discovery. By study and measurement of hundreds of quartz crystals from many locations, Steno discovered a law now known as the constancy of interfacial angles. This law is one of the fundamental tenants of the scientific study of crystals -- Crystallography.
Quartz is relatively abundant as colorless, transparent, uniform crystals of adequate size for lapidary uses. Quartz is somewhat brittle so it chips easily. The mineral has low dispersion and when faceted it produces little colored reflected light (we call fire), but it does have a high enough index of refraction that faceted stones are quite sparkly. Let's not get the crystal in stemware and chandeliers confused with quartz crystal. The former is a special formula of leaded glass that has a high index of refraction and is a man-made material, not a natural mineral.
The physical properties of quartz, combined with its relatively great abundance when compared to many other gem materials, allow it to be one of the most used raw gem minerals. Quartz is cut into beads and spheres, carved into many types of objects, from animals to abstract objects d'art. It is faceted into beads and variously shaped individual stones. Sometimes carving and faceting techniques are combined to produce positive- or negative-relief stones. Carving can be simple or very ornate. Another carving style produces cameos. Carving methods involve some type of abrasive powder, nowadays most often diamond imbedded in carving bits. Simple domed cabochons are often cut and applied as protective capping material for soft gemstones. This technique is commonly used with opal to produce "doublets".
History of lapidary use
Some examples of the use of quartz by lapidaries will illustrate how early man actually learned and perfected the lapidary trades. Although dating back to early Grecian times, the utilitarian use of carved rock crystal really became popular with the Romans. A list of items owned by Nero included wine jugs, cups, vases, and drinking cups carved from flawless quartz crystal. Lenses of rock crystal were used to concentrate the sun's rays to produce heat for cauterizing wounds and lighting fires, particularly sacrificial fires. In Mexico, a life-sized carving of flawless crystal in the form of a human skull was discovered in the Aztec ruins. It weighed almost 39 pounds. We don't know what religious use it had, if any. One of the Chinese emperors had colorless rock crystal doors to his throne room so that he might view his subjects while remaining warm in his heated area. But the art of quartz carving reached its zenith under the graces of Catherine the Great of Russia, who was a royal patron of this industry. Thousands of beautifully rendered art objects made from rock crystal and many other varieties of quartz were manufactured in old Russia. Perhaps the best known example in America is a seal showing Atlas holding the world. It was on display in the American Museum of National History in New York for many years. Generations of Chinese artisans have made lapidary contributions done through the centuries. The Chinese have specialized in exquisitely rendered miniature carvings made from colorless crystal, including vases, snuff bottles, ink boxes, incense burners, pendants, and figurines. Many other varieties of quartz have been utilized for the same purposes.
Crystal balls
However, no utilitarian object I've mentioned attracts more attention than flawless balls or spheres of quartz. Their manufacture dates far back into antiquity. The early Hindus, Greeks and Romans used small ones as reading balls (magnifiers). Small spheres are still quite popular today as gazing balls. Any flawless quartz sphere over 6 inches in diameter is usually out of reach, monetarily, of the average person. We know little of how the ancient Greek or Roman lapidaries made these reading balls. However, the extremely laborious methods of the ancient Japanese are well documented. The stone was roughly chipped to a spherical shape with hammer and chisel, then rolled in an iron trough with water and sand until perfectly round. Emery powder was used in a similar manner to produce a satin polish. Final polish was accomplished by the hand-rubbed application of rouge. In this manner, a finished sphere could be produced in a few years! Flawless quartz spheres are sometimes placed on display for all to view. At the Centennial Exposition in Philadelphia in 1876, a 7-inch diameter sphere from Japan was exhibited on a solitary stand. Around it were several cases of all types of ornaments carved of rock crystal. At this time a perfect 4 inch sphere from Japan might be purchased for $ 2,500. Another sphere, 6.5 inches in diameter, was on display at the Colombian Exposition in Chicago in 1893. It was valued at $ 10,000. Presently, the largest flawless quartz sphere in America is owned and displayed by the National Museum in the Smithsonian's Museum of Science and History -- Gem Hall, in Washington, D. C. It is 12 and 7/8ths inches in diameter and weighs 107 pounds. It was valued at around $ 250,000 in 1938! A trip to the Nation's Capital is not complete without visiting the National Museum and seeing both this sphere and the Hope diamond. They are displayed in the same room.
Inclusions in Rock Crystal
Inclusions of other minerals in rock crystal and smoky quartz are not particularly uncommon and are often highly attractive. They may be of two general types: early formed minerals that were captured by later formed quartz as it grew and minerals that were forming in or floating in the hydrothermal fluids that were deposited on the growing quartz crystal. Examples of the first type include rutile, actinolite, hedenbergite, some hematite, and tourmaline crystals that formed early and had rock crystal deposited over them, thereby encasing the early minerals. The latter type includes chlorite, cookeite, hematite, mica, pyrite, galena, adularia, and many others, that were deposited as the quartz was crystallizing. In some specific instances, such as asteriated quartz, rutile is thought to have been in solid solution in the quartz and, upon cooling, the rutile was forced out of the quartz structure, resulting in microscopic crystallographically oriented needles. The light, playing off these oriented needles, presents a six-ray star typical of asterism. The various types of included crystals give rise to a variety of lapidary materials and uses. Major sources for these types of gem materials are located in Brazil and Africa.
References
There are many books written that cover the various types of quartz, including rock crystal, but I think the following literature is some of the best around:
Quartz family minerals, a handbook for the mineral collector by Dake, Feener, and Wilson, 1938, McGraw-Hill Book Company, Inc., 304 p.
Quartz crystal in Brazil by Johnson and Butler, 1946, GSA Bulletin, 57:601-49.
The properties of silica by Sosman, 1927, New York, Chemical Catalog Company, Inc.,856p.
Quartz crystal deposits of western Arkansas by Engel, 1952, US Geological Survey Bulletin 973-E, p. 173-258.
An introduction to the rock-forming minerals by Deer, Howie, and Zussman, 1966, New York, John Wiley and Sons, Inc., 528 p.
Structure and vein quartz of the Ouachita Mountains of Oklahoma and Arkansas by Miser in The geology of the Ouachita Mountains -- A symposium , Dallas Geological Society and Ardmore Geological Society, p. 30-43.
See also Gemstones of the Bible
Ch 1, Page 13
Contact the authors of Rockhounding Arkansas Revised July 1998
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