mineral

Amethyst geode halves

Amethyst (紫色 quartz), silicon dioxide (SiO₂), colored by iron impurities and irradiation

AI-generated identification · may be incorrect

Purple, glassy quartz crystals lining cavities, with a white-to-gray chalcedony/quartz rind; Mohs hardness 7, vitreous luster, trigonal crystal structure, no cleavage, specific gravity about 2.65.

Identified August 27, 2026More mineral →

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Physical properties

Purple, glassy quartz crystals lining cavities, with a white-to-gray chalcedony/quartz rind; Mohs hardness 7, vitreous luster, trigonal crystal structure, no cleavage, specific gravity about 2.65.

Formation & geological history

Formed when silica-rich groundwater deposited quartz and amethyst crystals inside gas cavities of volcanic basalt, typically during the Cretaceous to Cenozoic eras. These appear cut and polished into matching geode halves.

Uses & applications

Used as ornamental display pieces, lapidary material, jewelry, and metaphysical collectibles; not generally used structurally. Value increases with vivid purple color, crystal size, completeness, and attractive symmetry.

Geological facts

Amethyst is the purple variety of quartz and is February’s birthstone. Prolonged heating can turn it yellow or orange, producing citrine-like material.

Field identification & locations

Identify by the crystalline quartz lining, purple coloration, and contrasting pale rind; dyed imitations may show unnaturally uniform color or concentrated pigment in fractures. Major sources include Brazil, Uruguay, Zambia, and Mexico.