mineral

Amethyst geode slice

Quartz (SiO₂), purple variety amethyst; commonly a volcanic vesicle geode

AI-generated identification · may be incorrect

Hardness 7 Mohs; white-to-gray chalcedony/quartz rind with purple crystalline quartz interior, vitreous luster, hexagonal crystals, and no prominent cleavage. Purple color comes mainly from iron impurities and irradiation.

Identified August 20, 2026More mineral →

Explore Amethyst geode slice in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits quartz and amethyst crystals inside cavities in basaltic volcanic rocks. Most commercial examples formed in Mesozoic–Cenozoic volcanic provinces, especially Brazil and Uruguay.

Uses & applications

Used as a decorative specimen, jewelry, cabochons, and crystal-collecting material; small slices commonly sell as affordable ornaments.

Geological facts

The outer band is typically microcrystalline quartz or chalcedony, while the cavity contains larger drusy crystals. Deeper violet color generally increases desirability, though natural color zoning is common.

Field identification & locations

Identify it by the hard, glassy purple quartz crystals lining a hollow, contrasting with a pale chalcedony rind; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, and Morocco.