This is much the most common and most widely distributed variety of quartz. It must have been known since prehistoric times, and the Greeks named it “crystal,” or ice, lieving it to be a form of the latter, irreversibly frozon by some process of extreme cold.
Appearance Although quite common, it has been used as a gemstone (albeit an inexpensive one) because of its beauty. It was and still is cut into all shapes, except, perhaps, the brilliant, which would mercilessly display its inferiority to diamond. It has been used much more frequently for the fashioning of elaborate, finely engraved cups, jugs,and vases. Veritable masterpieces were produced in the past and there are still places where the tradition is continued. Simpler pieces make use of quartz that has striking inclusions in the form of long, thin yellow-brown rutile needles or black tourmaline prisms, sometimes crossed in various ways. Such quartz specimens make attractive ornaments, despite being harder to work.
Distinctive features lt is distinguished from glass, particularly of the type sold under the name of lead crystal, by its birefringence. Glass also frequently contains minute air bubbles. Some difference in hardness (7 for quartz, no more than 5 for lead glass) may also help distinguish it.
Occurrence Large quantities of quartz come from Brazil and Madagascar, but the colorless variety is found almost everywhere. In the nineteenth century, magnificent objects were made from quartz discovered in the French and Austrian Alps.
Value As a gem, its value is extremely low. It is now cut almost exclusively for collectors and amateurs. As an or naﬁiental material, its value largely depends on the way in which it is fashioned. Fine examples may be quite valuable and more costly than similar pieces made from more opaque materials. Finely worked antique pieces are, of course, still more valuable.
Simulants and synthetics The confusion of lead crystal glass with rock crystal is generally due to misunderstand ing rather than imitation. Large amounts of synthetic quartz are produced nowadays, but only the amethyst and citrine varieties are of interest to the gem trade. The colorless variety is made only for technological purposes.