gemstone

Agate

Silicon dioxide (Chalcedony), SiO2

Hardness: 6.5-7 on the Mohs scale. Color: Varied, often translucent grayish-blue, brown, white, or banded. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None (exhibits conchoidal fracture). Specific gravity: 2.58-2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified August 2, 2026More gemstone →

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Physical properties

Formation & geological history

Formed by the deposition of silica from groundwater in the cavities of igneous and sedimentary rocks, often developing concentric bands over millions of years.

Uses & applications

Used in jewelry, ornamental carvings, decorative objects, and historically for precision instruments like mortar and pestles.

Geological facts

Agate has been used by humans since Neolithic times as gemstones and amulets. The name comes from the Achates River in Sicily where agates were found in antiquity.

Field identification & locations

Can be identified in the field by its waxy luster, smooth water-worn texture on beaches, translucency when held to light, and conchoidal fracture. Commonly found in riverbeds, beaches, and volcanic regions worldwide.