sedimentary

Agate

Silicon dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including grey, white, blue, red, green, and yellow, often in bands. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 6
Luster: Waxy to vitreous

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms primarily within metamorphic and igneous rocks, most commonly as nodules in volcanic rocks or ancient lavas where silica-rich groundwater deposits silica in hollow cavities layer by layer over millions of years.

Uses & applications

Used extensively in jewelry, ornamental carvings, polished display specimens, and industrial applications requiring durable precision instruments or mortars and pestles.

Geological facts

Agate was named by the Greek philosopher Theophrastus, who discovered the stone along the shoreline of the Achates River in modern-day Sicily.

Field identification & locations

Easily identified by its distinctive banded patterns, waxy luster, and translucent to opaque appearance. Found worldwide, with major deposits in Brazil, Uruguay, India, Madagascar, and the United States.