mineral

Banded agate (likely jasper/agate fragment)

Microcrystalline quartz, SiO₂, commonly chalcedony with iron-oxide and clay inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque brown, cream, gray, and black bands with a waxy to dull luster. Fibrous cryptocrystalline quartz lacks visible cleavage and typically has conchoidal fracture; the specimen appears naturally rough or partially polished.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz, often with iron staining. Individual agates may range from Paleozoic to Cenozoic in age, depending on their host rocks.

Uses & applications

Used for cabochons, beads, carvings, bookends, and decorative stone; small rough fragments have modest collecting value.

Geological facts

The banding records changing chemistry, temperature, and fluid flow during cavity filling. Its dark layers may contain manganese or iron oxides, while yellow-brown areas are likely limonite or other iron-bearing material.

Field identification & locations

Identify by curved/concentric bands, waxy appearance, very high hardness, and inability to scratch with a steel blade easily; common sources include volcanic regions of Brazil, Uruguay, Mexico, India, and the western United States.