Amethyst

Hardness: 7 on the Mohs scale; Color: Ranges from very dark purple to reddish-purple; Luster: Vitreous; Crystal Structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: Approximately 2.65

Amethyst is a variety of quartz that forms in hydrothermal veins and vugs (cavities) within volcanic rocks. It crystallizes from silica-rich fluids at relatively low temperatures. Much of the world's amethyst formed during the Mesozoic and Cenozoic eras.

Predominantly used as a gemstone in jewelry (rings, necklaces, earrings). Larger specimens are also popular for decorative purposes and as mineral collecting pieces.

Amethyst's purple color is due to irradiation of iron impurities within the quartz crystal. Heat treatment can change the color of amethyst to yellow, orange, or green, often sold as citrine or 'prasiolite' (green amethyst). It has long been associated with royalty and was believed to prevent intoxication.

In the field, amethyst can be identified by its distinctive purple color, vitreous luster, and hexagonal crystal habit (though often found as massive or geode fillings). It is commonly found in Brazil (especially Rio Grande do Sul), Uruguay, Bolivia, Siberia (Russia), Zambia, and Canada. For collectors, look for deep, uniform color and good clarity. Be cautious of heat-treated or synthetic amethyst.