Quartz Information
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WEARABILITY* Very Good
ENHANCEMENTS Irridation, dying, heat treatment for colored varieties only. Occasional.
*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It!
... Quartz is one of the most common minerals on earth. (See The X Factor.) It is well loved as amethyst, citrine, rose, and smoky quartz. There are many other natural varieties, plus synthetic quartz that comes in every color of the rainbow.
... The name quartz comes from the Greek, "krystallos," meaning ice. Amethyst also comes from a Greek word. "Amethystos," meaning "not drunk." It was believed one could drink all night and remain sober if they had an amethyst in their mouth. Citrine is from the French, "citrin," meaning yellow.
CHEMISTRY SiO2
CRYSTALLOGRAPHY Hexagonal
REFRACTIVE INDEX 1.544 - 1.553
HARDNESS 7
SPECIFIC GRAVITY 2.651
CLEAVAGE None
HEAT SENSITIVE No
SPECIAL CARE INSTRUCTIONS None
For more details see the article on "Hardness and Wearability."
... Rock crystal, colorless quartz, is rarely used as a gem. However, it is prized by carvers and frequently used as caps for triplets.
... Amethyst ranges from a light, pinkish violet to an opaque purple. The lightest shades are called "Rose de France." While currently out of vogue, they have traditionally been very fashionable. Today, the variety most in demand is "Siberian." That does not refer to its origin, but to dark purple coloring, with flashes of red or blue.
... Citrine is the yellow to orange variety of quartz. These are the colors traditionally associated with topaz, and they are still confused by many. Its color ranges from a light lemon yellow, to a rich orange. "Madeira" citrine is a strong orange color, with red flashes. It is created by heat treating citrine with the proper iron content and demands the highest price.
... Relatively new on the market is ametrine, with zones of both purple and yellow. The colors only reach a medium level of saturation and are never very dark. Cutting the material so both color show is sometimes a challenge for the lapidary. However, a well cut, bi-colored gem is a real delight. Ametrine is only found in Bolivia.
... Smoky quartz is also mistaken for topaz. It comes in every shade of brown, from a light tan to nearly black. "Chocolate citrine" is a pleasant brownish/yellow color. Smoky quartz is known for its large sizes. The person who wants a really big gem, without a really big budget, often ends up with one of these.
... Rose quartz receives its coloring from titanium. It is always a light to medium pink, but sometimes is influenced by amethyst and picks up a violet shade. Until the 1980's, when a new deposit was discovered in Madagascar, it was never found completely transparent. Indeed, one of its best uses is for star cabs and spheres.
... Tyndall scattering is one of the rarest phenomena in gemology, but it is relatively common in Madagascar rose quartz. Tyndall scattering is where light is dispersed by fine particles and produces a blue color. This is the same as what happens when sunlight hits dust particles in the air and why the is sky blue. In rose quartz, you see both pink and blue in the same tone.
... While these are the most common varieties, they in no way exhaust the range of crystalline quartz. With the addition of inclusions, the list is nearly endless. In addition, there are stars and cats eye gems in this rich family of gemstones.
... Quartz is an unusual mineral. It is stable below 573 degrees Centigrade, but between 573 and 870 degrees, tridymite, (another silica mineral,) forms. At 1470 degrees, tridymite undergoes a structural rearrangement and becomes cristobalite, which is isometric. At 1710 degrees, cristobalite melts to a viscous liquid. If cooled quickly, it forms silica glass with no internal structure.
... Tridymite and cristobalite have no gem significance; except that the "snowflakes" sometimes found in obsidian are cristobalite.
... Quartz grows in primarily in pegmatites, but is hydrothermal grown in laboratories. Quartz grows very large, with cut gems in the thousands of carats. The exceptions are amethyst, which rarely produces a clean gem of 100 carats, and rose quartz, which rarely exceeds 30 carats in a transparent gem. Translucent specimens can weigh several pounds.
... Quartz is one of the first gems to be synthetically grown on a large scale. Major development was done during World War II, to supply crystals for radios. Today, our computer industry is based on synthetic quartz. Not that there is a shortage of natural crystals, but the synthetics are always clean and are less time consuming to trim into the necessary pieces.