mineral

Amethyst stalactite slice / amethyst geode

Quartz, SiO₂; purple coloration from trace iron and irradiation

AI-generated identification · may be incorrect

Hardness 7 Mohs; vitreous luster; purple quartz crystals surrounding a polished, banded agate/chalcedony center. Quartz is trigonal, lacks cleavage, and has specific gravity about 2.65.

Identified August 16, 2026More mineral →

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Physical properties

Hardness 7 Mohs; vitreous luster; purple quartz crystals surrounding a polished, banded agate/chalcedony center. Quartz is trigonal, lacks cleavage, and has specific gravity about 2.65.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing concentric chalcedony/agate followed by amethyst crystals; most commercial material is Cretaceous–Tertiary in age. Major sources include Brazil and Uruguay.

Uses & applications

Used as a decorative specimen, ornamental slice, and jewelry material; intact crystal clusters and vividly banded geodes are popular collectibles.

Geological facts

The central cavity commonly preserves agate bands and later quartz growth, recording changing fluid chemistry. Heating amethyst can turn it yellow-orange, producing citrine-like material.

Field identification & locations

Identify by purple, glassy quartz crystals, hardness that scratches glass, and concentric agate banding around a cavity; it is not generally magnetic. Value is typically $30–$200 for attractive slices, with large exceptional specimens reaching $500–$2,000+.