ROCK CRYSTAL, the clear and colorless variety of quartz

VARIETY INFORMATION:
VARIETY OF: Quartz , SiO 2 , Silicon Dioxide .
USES: Ornamental stone and gemstone.
COLOR: Colorless.
INDEX OF REFRACTION: 1.544-1.553
BIREFRINGENCE: 0.009
HARDNESS: 7
CLEAVAGE: none
CRYSTAL SYSTEM: trigonal

Rock crystal is the name given to all clear colorless quartz. It is widely used as a popular ornamental stone and is also used as a gemstone. Although it is one of the lest expensive gemstones, cut rock crystal has been used as imitation diamonds. Rock crystal lacks the fire, color (of course) and the rarity to be ranked as a fine precious gemstone. None-the-less, rock crystal is in wide use as a gemstone due to its beauty, affordability, availability and ease of cutting.
The most use for rock crystal is in ornamental carvings. The most well known ornamental carving for rock crystal is the crystal ball of fortune telling fame. While rock crystal is common it is hard to find large crystals of quartz with the clarity and size required for crystal balls that most of us associate with fortune tellers.Rock crystal is used for many ornamental carvings from spheres (crystal balls) to pyramids to obelisks to figurines to eggs to bowls to wands. There are many fine chandeliers that are outfitted with rock crystal ornaments.

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Many people prefer uncut clusters of rock crystal. These natural treasures look like crystal cities of fantasy stories. The long slender clear prisms of quartz projecting upward from a common base are true mineralogic wonders that can be admired by all. They cost of good clusters of rock crystal is still affordable and comes from sources around the world.The best rock crystal sources are in the famous Hot Springs area of Arkansas, USA; Cumberland, England; St. Gotthard, Switzerland; Brazil and Madagascar.Large individual crystals of quartz have been found in Brazil, the largest weighs over 44 tons.

Rock crystal often has inclusions of other minerals and these inclusions sometimes produce popular varieties of ornamental stone. Golden rutile inclusions produce a unique stone aptly named rutilated quartz that has a very hair-like look. Another apply named stone is called tourmalinated quartz and contains intricatly crossing needles of black schorl tourmaline trapped in the clear crystal.
Phantoms are a result of inclusions which occur when other minerals such as chlorite, hematite or even milky quartz form as a crust on the surface of the crystals during an hiatus in the crystal's growth. The crystal then grows out and around the encrusting growth encasing it inside. But since the thin encrustations formed over a crystal complete with crystal faces it appears that there is a crystal inside the crystal. The encrustations are often incomplete or diffuse and appear ghostly, hence the name phantom.

Rock crystal is only one of several quartz varieties. Other varieties that form macroscopic (large enough to see) crystals are as follows:

Amethyst is the purple gemstone variety.
Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst.
Milky Quartz is the cloudy white variety.
Prasiolite is the leek-green variety.
Rose quartz is a pink to reddish pink variety.
Smoky quartz is the brown to gray variety.

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