mineral

Banded agate (likely chalcedony)

Agate, microcrystalline quartz (SiO₂), commonly with chalcedony and quartz layers

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; gray, cream, and white concentric banding; waxy to vitreous luster; cryptocrystalline structure with no obvious cleavage. Specific gravity is about 2.60–2.65.

Identified August 19, 2026More mineral →

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Physical properties

Hardness 6.5–7 Mohs; gray, cream, and white concentric banding; waxy to vitreous luster; cryptocrystalline structure with no obvious cleavage. Specific gravity is about 2.60–2.65.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz. Individual bands may form over long intervals, commonly in Cenozoic or older volcanic terrains.

Uses & applications

Used for cabochons, carvings, bookends, ornamental objects, and polished slices; this rough specimen has modest collector value.

Geological facts

The curved, “fortification” banding is characteristic of agate and records changing chemistry during cavity filling. Creamy opaque areas may contain microcrystalline quartz, clay, or iron-oxide impurities.

Field identification & locations

Identify by testing for glass-scratching hardness, examining the translucent layered bands, and checking its low reaction to dilute acid. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and volcanic regions worldwide.