mineral

Iron-stained agate/chalcedony nodule

Microcrystalline quartz (SiO₂), likely agate with hematite/goethite inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent gray, orange, brown, and reddish zones with waxy to glassy luster. Quartz is trigonal but occurs here as cryptocrystalline bands; no obvious cleavage, conchoidal fracture, and moderate-to-high density (~2.6 g/cm³).

Identified August 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled cavities in volcanic rock, depositing successive layers of chalcedony; iron oxides produced the red-brown staining. The exact age depends on its source locality, commonly Mesozoic or Cenozoic volcanic terrain.

Uses & applications

Used as a decorative stone, cabochon, lapidary material, and collectible; harder, well-patterned pieces may be polished for jewelry or display.

Geological facts

The gray translucent portion is typical chalcedony, while rusty colors commonly indicate hematite or goethite. A strong light may reveal internal translucency and subtle banding.

Field identification & locations

Identify by hardness, waxy translucence, conchoidal fracture, and resistance to scratching by steel; vinegar produces no reaction. Common worldwide, especially in volcanic regions of Brazil, Uruguay, Mexico, the United States, and Australia.