mineral

Amethyst geode

Quartz (SiO₂), purple variety amethyst; commonly hosted in basalt

AI-generated identification · may be incorrect

Hardness 7 Mohs; purple to lilac drusy crystals with vitreous luster, hexagonal crystal structure, and no cleavage. The gray-blue outer rind is likely chalcedony and weathered basalt; specific gravity is about 2.65 for quartz.

Identified September 6, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits quartz crystals inside gas cavities in volcanic basalt, with iron impurities producing the purple color through irradiation and heating. Most commercial geodes formed in Mesozoic–Cenozoic volcanic provinces, especially Brazil and Uruguay.

Uses & applications

Used for ornamental display, lapidary work, jewelry, and metaphysical collecting; large cavity specimens are popular décor pieces.

Geological facts

Amethyst color can fade with strong sunlight or heating. Crystal intensity commonly varies from pale lilac at the rim to deep purple in sheltered cavity areas.

Field identification & locations

Identify by the hollow cavity lined with sparkling purple quartz crystals, glassy luster, and hardness sufficient to scratch ordinary glass; common sources include Brazil, Uruguay, Mexico, and Morocco.