mineral

Amethyst geode cluster

Quartz (SiO₂), purple variety amethyst, with a banded agate/chalcedony center

AI-generated identification · may be incorrect

Amethyst has Mohs hardness 7, vitreous luster, hexagonal quartz crystals, and no cleavage; purple crystals surround concentric gray, white, and orange chalcedony bands. Color comes mainly from iron impurities and natural irradiation.

Identified October 13, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich fluids filled a cavity in volcanic rock; quartz crystals and chalcedony bands grew over time. Such geodes commonly formed in basalt during the Cretaceous, roughly 100 million years ago, though age varies by locality.

Uses & applications

Used for mineral collecting, display, and jewelry; amethyst is also cut into cabochons and beads.

Geological facts

The central eye-like banding is agate, a microcrystalline form of quartz, while the sparkling outer points are amethyst crystals.

Field identification & locations

Identify it by purple, pointed quartz crystals lining a cavity and a banded chalcedony center; notable sources include Brazil and Uruguay. Avoid acidic cleaners and protect the color from prolonged strong sunlight.