3.5" Amethyst Crystals on Sparkling Quartz Chalcedony - India

Amethyst is a purple variety of quartz (SiO2) that owes its violet color to natural gamma irradiation, iron impurities, and the presence of trace elements, which result in complex crystal lattice substitutions. It is considered a semi-precious gemstone, and just two centuries ago was considered to have a value on par with diamonds, sapphires, and rubies. The largest and best known amethyst deposits occur in southern Brazil and Uruguay, where they are found in hydrothermally-formed geodes, but many localities around the world produce an amazing variety of amethyst crystals and formations. They are almost always formed in medium- to high-temperature geological settings.

Chalcedony is any microcrystalline variety of silica composed of very fine intergrowths of quartz and mogánite: microcrystalline minerals have microscopic crystals that cannot be observed by the naked eye. Both quartz and mogánite have the same chemical formula SiO2 (silicon dioxide), but different crystal structures. When free from impurities, chalcedony is colorless and transparent. Depending on impurities present during formation, chalcedony can form in a wide variety of colors including red, yellow, green, blue, purple, grey, white, and numerous hues in between. Chalcedony is quite hard at 7 on the Mohs Hardness Scale: this matches its main component quartz, which is the benchmark mineral for the scale at 7.