mineral

Banded Agate (Polished Slice)

Chalcedony (cryptocrystalline Quartz), SiO2

Hardness: 6.5–7 on the Mohs scale. Color: Multicolored concentric bands (black, gold/yellow, white, and translucent grey). Luster: Waxy to vitreous. Crystal Structure: Trigonal (microscopic). Specific Gravity: 2.58–2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary deposits in volcanic rock cavities (vesicles) or metamorphic rocks. Silica-rich groundwater percolates through hollows, depositing layers of microcrystalline quartz over thousands of years. Often dating from the Cenozoic to the Precambrian depending on the host rock.

Uses & applications

Commonly used in jewelry (cabochons), lapidary art, decorative coasters, bookends, and precision instruments like mortar and pestles due to its hardness and resistance to chemicals.

Geological facts

The name comes from the Achates River in Sicily, where agates were first found in ancient times. The distinct bands are caused by variations in the mineral impurities (like iron or manganese) present during the layering process.

Field identification & locations

Identify in the field by looking for nodular, waxy-textured rocks with concentric banding visible when chipped or sliced. Common locations include Brazil, Uruguay, Germany, and the Lake Superior region of the USA.

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