mineral

Polished agate (likely fortification or plume agate)

Microcrystalline quartz/chalcedony, SiO₂, with iron-oxide inclusions

AI-generated identification · may be incorrect

Cream, tan, and honey-brown translucent banding with fine curved layers and a gray included zone; waxy to glassy luster. Mohs hardness about 6.5–7, no cleavage, conchoidal fracture, trigonal quartz structure; specific gravity about 2.6.

Identified September 17, 2026More mineral →

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At a glance

Common name: Polished agate (likely fortification or plume agate)
Scientific name: Microcrystalline quartz/chalcedony, SiO₂, with iron-oxide inclusions
Category: mineral
Identified: September 17, 2026
Method: Standard

AI Estimated Value

Approximately $10–$60 for a small polished specimen; $75–$200+ if unusually large, attractive, or confirmed from a collectible locality.

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

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive chalcedony layers. The pictured piece is cut and polished; its exact geological age and source cannot be determined from the image.

Uses & applications

Used for cabochons, carvings, ornaments, lapidary pieces, and collector specimens; durable but relatively common material.

Geological facts

The curved “fortification” bands record repeated changes in fluid chemistry during cavity filling. Gray areas may be included host material or contrasting chalcedony rather than a separate mineral.

Field identification & locations

Identify by hardness, translucent edges, waxy luster, and persistent curved bands; it should scratch glass but not be scratched by a steel knife. Agate is common worldwide, including volcanic terrains of coastal California, though this exact variety cannot be localized visually.