mineral

Polished banded agate (likely seam or fortification agate)

Microcrystalline quartz, SiO₂ (chalcedony with agate banding)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown, tan, cream, and reddish bands with waxy-to-glassy luster and translucent edges. Quartz is trigonal, but crystals are microscopic; no obvious cleavage, conchoidal fracture, and specific gravity about 2.6.

Identified August 17, 2026More mineral →

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At a glance

Common name: Polished banded agate (likely seam or fortification agate)
Scientific name: Microcrystalline quartz, SiO₂ (chalcedony with agate banding)
Category: mineral
Identified: August 17, 2026
Method: Standard

AI Estimated Value

Approximately $10–$60 for a common polished specimen of this size; $75–$200+ if the banding, translucency, workmanship, or provenance 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 and fractures, depositing successive layers of chalcedony and quartz. Agate formation spans many geological ages, commonly in volcanic rocks from the Paleozoic to Cenozoic.

Uses & applications

Used for cabochons, carvings, beads, bookends, and ornamental objects; polished specimens are popular collectibles. Common material generally has modest commercial value.

Geological facts

The curved parallel bands record repeated changes in fluid chemistry during cavity filling. Iron oxides commonly create the red, orange, and brown coloration.

Field identification & locations

Identify by curved or concentric fine banding, waxy polish, translucency, and quartz-like hardness; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.