mineral

Polished banded agate slab

Agate, microcrystalline quartz (SiO₂), commonly with chalcedony and minor quartz, iron oxides, and other trace minerals

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; waxy to vitreous luster; translucent gray, blue, cream, and brown concentric banding; cryptocrystalline quartz with no cleavage, conchoidal fracture, and specific gravity about 2.6. The specimen is cut and polished, likely a decorative half-slice.

Identified August 29, 2026More mineral →

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At a glance

Common name: Polished banded agate slab
Scientific name: Agate, microcrystalline quartz (SiO₂), commonly with chalcedony and minor quartz, iron oxides, and other trace minerals
Category: mineral
Identified: August 29, 2026
Method: Standard

AI Estimated Value

Approximately $20–$100 for a small polished slab; unusually large, vivid, well-patterned pieces may sell for $150–$500 or more.

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, depositing chalcedony and quartz in successive layers. Individual agates may form over extended geological periods, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, jewelry, ornaments, bookends, and polished display slabs; valued primarily for attractive pattern, color, size, and polish.

Geological facts

The sharply contrasting concentric bands are characteristic of fortification agate. Blue or purple coloration may be natural or enhanced by treatment, and the exposed edge can reveal the original cavity-filling sequence.

Field identification & locations

Identify by curved, repeating bands, very hard glassy surfaces, and conchoidal edges; it will scratch glass but not be scratched easily by a steel knife. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the United States.