sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale. Color: Variable, including white, gray, blue, red, green, and yellow, often with banded patterns. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.60 to 2.65.

Hardness: 6
Luster: Waxy to vitreous

Identified August 4, 2026More sedimentary →

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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 over millions of years.

Uses & applications

Used widely in ornamental objects, jewelry, tumbled stones, as well as industrial applications like precision instruments, mortars, and pestles due to its hardness.

Geological facts

Agate is one of the most common materials used in the art of lapidary. Ancient civilizations such as the Greeks and Egyptians used agates for rings, seals, and healing amulets, believing it protected against storms and thirst.

Field identification & locations

Can be identified by its distinctive banded patterns, waxy luster, and conchoidal fracture. Commonly found in regions with ancient volcanic activity, such as Brazil, India, Madagascar, and the USA (e.g., Lake Superior region).