The name "Amethyst" comes from the Greek word meaning "against drunkenness." This was perhaps due to a belief that amethyst would ward off the effects of alcohol, but most likely the Greeks were referring to the wine-like color of some varieties of the stone. Amethyst is the purple variety of the mineral quartz and is a popular gemstone. Amethyst can occur as elongated prismatic crystals which have a six sided pyramid at either end. They can also form as druzes that are crystalline crusts that only show the pointed terminations of each crystal. The color purple has long been associated with royalty, making amethyst jewelry a popular choice among royal families.
The "Amethyst" variety of quartz derives its purple color from trace amounts of iron that have been oxidized from exposure to naturally occurring ionizing-radiation that is a byproduct of the decay of potassium 40.
Amethyst has a hardness of 7 on the Mohs scale. The Toughness of Amethyst is Good. Amethyst crystalizes in the hexagonal crystal system (trigonal-trapezohedral), with an "Enantiomorphic" Crystal Habit, forming left-right (Japan Law) twins (photo below). Amethyst has a refractive index of 1.544. Amethyst can also occur as drusy masses or encrustations, showing only the rhobohedral termination points. Amethyst is typically associated with igneous rock.
Amethyst belongs to the quartz family of minerals, and is classified as a Tectosilicate. Quartz is one of the most commonly found minerals within the earth's crust. The chemical Silica Dioxide is the principle component in quartz as well as most other igneous rocks. Amethyst is formed from silica rich liquids deposited in gas cavities or geodes within lava.
Chemical composition: SiO2
Ametrine Gemstones
A rare bi-colored variation of citrine and amethyst called "Ametrine" was recently discovery in Bolivia. Ametrine is a naturally occurring variety of quartz that contains both amethyst and citrine that are colored by trace elements of Fe3 (citrine yellow) and Fe4 (amethyst purple) iron ions. The only major source for Ametrine in the world is from the Anahí Mine in Santa Cruz, Bolivia.
Ametrine has a color transition that is similar to tourmaline, but with the distinct amethyst purple and citrine gold colors. There is also a synthetic Ametrine coming out of Alexandrov, Russia.
Further Reference on Ametrine: Caltech - Ametrine
