mineral

Chalcedony geode (likely amethyst-bearing)

Microcrystalline quartz, SiO₂; purple coloration from trace iron and irradiation

AI-generated identification · may be incorrect

Hardness 7 Mohs, vitreous to waxy luster, gray-purple chalcedony rind, and a hollow cavity lined with tiny druzy quartz crystals. Quartz is trigonal; it has no cleavage and conchoidal fracture, with specific gravity about 2.60–2.65.

Identified September 2, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled vesicles or cavities in volcanic rock, depositing chalcedony and later quartz crystals. The specimen is likely Cenozoic or younger, though its exact age cannot be determined from the photograph.

Uses & applications

Used as a decorative specimen, lapidary material, and occasional jewelry stone; larger amethyst geodes are valued for display and interior décor.

Geological facts

The dark purple interior may be amethyst, but the image is insufficient to confirm the color intensity or mineral identity. A rough outer rind commonly preserves the original volcanic cavity shape.

Field identification & locations

Identify by its rounded cavity, waxy gray chalcedony, and sparkling quartz lining; common sources include Brazil, Uruguay, Mexico, and Morocco. Avoid acid testing; a steel file should not scratch quartz.