mineral

Amethyst with Marcasite accents

Amethyst (Silicon Dioxide SiO2) and Marcasite (Iron Sulfide FeS2)

Amethyst: Hardness of 7 on Mohs scale, violet/purple color, vitreous luster, hexagonal (trigonal) crystal system. Marcasite (likely jeweler's marcasite/pyrite): Hardness 6-6.5, brassy metallic luster, orthorhombic structure.

Identified March 13, 2026More mineral →

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Physical properties

Formation & geological history

Amethyst forms in geodes or cavities within igneous rocks through hydrothermal processes. The purple color comes from irradiation of iron impurities. Marcasite forms in low-temperature hydrothermal veins or sedimentary environments.

Uses & applications

Predominantly used as a gemstone in jewelry (pendants, rings, earrings). Amethyst is also a popular collector's mineral and is associated with the February birthstone.

Geological facts

Amethyst was once considered one of the 'Cardinals' or most precious gems until large deposits were found in Brazil. 'Marcasite' in jewelry is usually actually the mineral Pyrite, as true Marcasite is unstable and can disintegrate when exposed to air.

Field identification & locations

Identify in the field by its distinct purple hue and quartz crystal habit. Primarily found in Brazil, Uruguay, Zambia, and Ontario. Collectors look for deep 'Siberian' purple saturation and clarity.

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