gemstone

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including white, gray, blue, red, orange, and brown, often exhibiting distinct concentric banding. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.58 to 2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified August 1, 2026More gemstone →

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Physical properties

Formation & geological history

Formed primarily within the cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions, usually in concentric layers around a core.

Uses & applications

Used extensively in jewelry, ornamental carvings, polished display specimens, precision instruments, and mortar and pestle sets due to its hardness.

Geological facts

Agates are among the oldest known gemstones, used by ancient civilizations like the Greeks and Egyptians for amulets, seals, and ornate vessels. The name comes from the Dirillo River (historically called Achates) in Sicily.

Field identification & locations

Easily identified by its characteristic curved or concentric banding patterns and waxy luster. Found worldwide, with notable deposits in Brazil, Uruguay, India, and various regions of the United States.