Amethyst
Image: Natural History Museum of Gagliole (CC0)
Mineral NameAmethyst
Chemical FormulaSiO2
Mohs Hardness7
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.65
Colorspurple, violet, lavender
Transparencytransparent to translucent
Type LocalityBrazil, Uruguay (common sources for large geodes)
Mineral GroupSilicates
Usesjewelry, ornamental, collector, spiritual
Associated Mineralschalcedony, calcite, goethite, hematite
Rarityuncommon
Description
A massive geode, hollowed out to reveal a sparkling interior densely covered with numerous deep purple amethyst crystals, contrasting with the dull, dark exterior rock.
Geological Context
Amethyst forms in the cavities of volcanic rocks, such as basalt flows, where silica-rich fluids deposit quartz crystals. The distinctive purple color is caused by trace amounts of iron impurities and natural irradiation.
