mineral

Agate

Banded Chalcedony (SiO2 - Silicon Dioxide)

Hardness: 6.5–7 on Mohs scale. Color: Multicolored concentric bands (gray, white, yellow). Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (Trigonal). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Multicolored concentric bands (gray, white, yellow)
Luster: Waxy to vitreous

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily within volcanic and metamorphic rocks. It occurs as a secondary mineral filling cavities (vesicles) in igneous rocks. As silica-rich water percolates through these cavities, layers of microcrystalline quartz are deposited over thousands of years.

Uses & applications

Commonly used in jewelry (cabochons, beads), decorative arts, and industrial precision tools like mortars and pestles due to its hardness and resistance to chemical attack.

Geological facts

Agate was named by Theophrastus, a Greek philosopher, who discovered the stone along the Achates River in Sicily. It has been used as a gemstone since the Neolithic era.

Field identification & locations

Identify in the field by its translucent properties and distinct concentric banding. It is often found as a rounded 'nodule' with a rough, weathered exterior. Common locations include Brazil, Uruguay, India, and the United States (Lake Superior region).