mineral

Amethyst geode

Quartz, SiO₂; purple variety: amethyst

AI-generated identification · may be incorrect

A hollow, roughly spherical geode lined with dark purple-to-gray quartz crystals and a thin banded chalcedony rim. Quartz has Mohs hardness 7, vitreous luster, hexagonal crystal structure, no cleavage, and specific gravity about 2.65; the exterior appears weathered and iron-stained.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed when gas cavities in volcanic basalt or other vesicular lava were later filled by silica-rich groundwater; chalcedony crystallized first, followed by quartz and amethyst. Geode formation commonly occurred in Cenozoic to Mesozoic volcanic terrains, though the exact age is specimen-dependent.

Uses & applications

Used as a decorative mineral specimen, bookend, or jewelry material when cut; large attractive geodes can be valuable display pieces.

Geological facts

Purple color generally results from trace iron activated by natural irradiation. Very dark interiors may be quartz with limited amethyst coloration or iron/manganese staining.

Field identification & locations

Identify by the hollow cavity, concentric chalcedony rind, and inward-pointing quartz crystals; common sources include Brazil, Uruguay, Mexico, and the United States. Avoid acids and inspect for artificially dyed color, especially if vivid purple is concentrated along fractures.