mineral

Polished brown agate/chalcedony nodule

Microcrystalline quartz (SiO₂), likely brecciated or weathered agate with possible carbonate/iron-oxide inclusions

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; brown, tan, cream, and rusty-red coloration; waxy to subvitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The porous, pitted areas may indicate vugs or altered host material.

Identified September 12, 2026More mineral →

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At a glance

Common name: Polished brown agate/chalcedony nodule
Scientific name: Microcrystalline quartz (SiO₂), likely brecciated or weathered agate with possible carbonate/iron-oxide inclusions
Category: mineral
Identified: September 12, 2026
Method: Standard

AI Estimated Value

About $5–$30 as a common polished specimen; $30–$100+ if its pattern, locality, size, or polish is exceptional.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, often producing banded chalcedony and agate; iron oxides create the reddish-brown colors. Agates commonly formed during the Cenozoic or older volcanic episodes, but this specimen’s exact age is unknown.

Uses & applications

Used as a lapidary stone for cabochons, carvings, tumbled stones, and decorative objects; generally ornamental rather than industrial.

Geological facts

Its rounded shape and smooth surface indicate natural stream or beach abrasion, possibly followed by light polishing. The irregular internal pattern is typical of an agate or chalcedony nodule rather than a crystalline quartz cluster.

Field identification & locations

Identify by testing hardness against glass, observing waxy chalcedony, and checking for conchoidal fracture; it should not be scratched by a steel knife easily. Common in volcanic regions and gravel deposits worldwide, especially Brazil, Uruguay, Mexico, India, and the western United States.