Amethyst

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Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek a- ("not") and μέθυστος methustos ("intoxicated"), a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief that it would prevent intoxication.

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Chemistry

Amethyst is the violet variety of quartz; its chemical formula is SiO2.

In the 19th century, the color of amethyst was attributed to the presence of manganese. However, since it is capable of being greatly altered and even discharged by heat, the color was believed by some authorities to be from an organic source. Ferric thiocyanate has been suggested, and sulfur was said to have been detected in the mineral[citation needed].

The color in amethyst is due to irradiation, which caused the iron ions present as impurities in quartz to rearrange themselves in the crystal lattice affecting the color in a reversible process.[1] Synthetic amethyst is thus man-made by gamma-ray, x-ray or electron beam irradiation of clear quartz which has been first doped with ferric impurities.

On exposure to heat, the irradiation effects can be partially cancelled and amethyst generally becomes yellow or even green, and much of the citrine, cairngorm, or yellow quartz of jewelry is said to be merely "burnt amethyst".[2]

Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are so similar to that of natural amethyst that it can not be differentiated with absolute certainty without advanced gemnological testing (which is often cost-prohibitive). There is one test based on "Brazil law twinning" (a form of quartz twinning where right and left hand quartz structures are combined in a single crystal[3]) which can be used to identify synthetic amethyst rather easily. It is possible to synthesize twinned amethyst, but this type is not available in large quantities in the market.[4]

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