mineral

Banded Chalcedony (Agate)

Chalcedony (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5–7 on Mohs scale. Color: Translucent white to tan with distinct banding. Luster: Waxy to vitreous. Crystal Structure: Trigonal/Monoclinic (microscopic). Cleavage: None (Conchoidal fracture). Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Translucent white to tan with distinct banding
Luster: Waxy to vitreous

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous rocks or sedimentary layers. They primarily develop in volcanic vesicles (gas bubbles) or cracks in the earth's crust, often dating from various geological periods from the Archean to the Cenozoic.

Uses & applications

Commonly used in lapidary work for cabochons, beads, and ornamental carvings. Historically used for mortar and pestles due to its hardness, and in industrial precision bearings.

Geological facts

Agate is the first gemstone mentioned in ancient history, used by Egyptians for amulets before 3000 B.C. The banding is caused by rhythmic crystallization cycles of silica and impurities during formation.

Field identification & locations

Identify in the field by its translucent edges, waxy texture, and unique concentric or parallel banding when broken. Commonly found in river beds, beaches, and volcanic regions (Pacific Northwest, Great Lakes, Brazil). To collect, look for stones with a 'potato-like' exterior that show glass-like translucency when wet.

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