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Rock Crystal
Rock Crystal is the clear colourless (whitte) form of the mineral quartz. As such it is related to amethyst which is the purple form of quartz, and also to citrine which is the yellow variety.
It owes its name to the ancients Greeks who found it in caves near Mount Olympus, and called it krustallos meaning ice, as they believed it to be water which had been permanently frozen by the gods.

Worth A Fortune?
Originally the crystal balls used by clairvoyants were made of rock crystal, but nowadays are usually made of glass.
Rock crystal is often carved into quite large ornaments, ancient and antique examples may be quite valuable.

Jewellery
Rock crystal has been used for jewellery, often as as imitation for diamond, and is still cut and polished into beads.

Hardness
The hardness of rock crystal is 7, and appears on the Moh scale as quartz.

Technical Details
Chemical Composition and NameSiO2 - Silicon Dioxide
Hardness7
Refractive Index1.544 - 1.553
Bi-refringence0.009
Specific Gravity2.65 - 2.66
Crystalline SystemTrigonal (Rhombohedral)
Optic SignPositive
Other Optical PropertiesUniaxial


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