mineral

Banded agate (likely carnelian/chalcedony nodule)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide staining

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown, reddish-orange, and gray translucent areas with waxy to dull luster. Fibrous cryptocrystalline quartz, lacking visible cleavage; specific gravity about 2.58–2.65.

Identified August 28, 2026More mineral →

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Physical properties

Hardness 6.5–7 Mohs; brown, reddish-orange, and gray translucent areas with waxy to dull luster. Fibrous cryptocrystalline quartz, lacking visible cleavage; specific gravity about 2.58–2.65.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony and quartz, later colored by iron oxides. Individual nodules commonly formed during Cenozoic volcanic activity, though age depends on locality.

Uses & applications

Used for cabochons, beads, carvings, and ornamental objects; attractive patterned pieces have modest jewelry and collector value.

Geological facts

The reddish color is typically caused by hematite or limonite inclusions. Agate’s banding is revealed most clearly by cutting and polishing.

Field identification & locations

Identify by its rounded nodule shape, translucency at thin edges, waxy surface, and curved or irregular banding; common sources include Brazil, Uruguay, India, Mexico, and the western United States. A rough specimen like this is usually worth $5–$30, while attractive polished material may sell for $20–$100+.