mineral

Polished/tumbled banded agate slab

Chalcedony (microcrystalline quartz), SiO₂, with iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; tan, cream, brown, and gray coloration with irregular concentric or cloudlike banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The plastic packaging and smooth surface suggest a cut and polished specimen.

Identified September 22, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony in successive layers, commonly during the Cenozoic or older volcanic episodes. Exact locality and age cannot be determined from the photograph.

Uses & applications

Used for cabochons, carvings, bookends, decorative slabs, and lapidary objects; attractive patterned material has modest jewelry and collecting value.

Geological facts

Agate patterns develop from changing chemistry, fluid flow, and impurities during cavity filling; each slice may reveal a different pattern.

Field identification & locations

Identify by its fine-grained quartz texture, waxy polish, lack of cleavage, hardness, and layered or mossy internal patterns; common sources include Brazil, Uruguay, Mexico, Madagascar, India, and the western United States.