gemstone

Agate

Silicon dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale. Color: Variable, often white, grey, blue, orange, red, or brown with banded patterns. Luster: Vitreous to waxy. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 6
Luster: Vitreous to waxy

Identified July 28, 2026More gemstone →

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Physical properties

Formation & geological history

Forms primarily within cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions, usually in concentric layers over long periods.

Uses & applications

Used in jewelry, ornamental carvings, polished specimens, mortars and pestles for laboratories, and by mineral collectors.

Geological facts

Agates are often found in ancient volcanic lava vesicles. The name comes from the Achates River in Sicily, where agates were found in antiquity.

Field identification & locations

Can be identified by its waxy luster, hardness (scratches glass), and distinctive translucent bands or patterns. Found worldwide, notably in Brazil, Uruguay, India, Madagascar, and the US.