sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, and a specific gravity around 2.60 to 2.65. Colors vary widely including white, gray, blue, purple, pink, red, orange, yellow, brown, and black, often exhibiting distinct conc…

Identified August 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily within the cavities of volcanic and metamorphic rocks through the slow deposition of silica-rich groundwater solutions over millions of years.

Uses & applications

Widely used for making ornamental objects, jewelry, tumbled stones, carvings, and in industrial settings for mortars and pestles due to its durability.

Geological facts

Agate was named by the Greek philosopher Theophrastus after the Achates river in Sicily, where stones were found in ancient times. It has been used for talismans and ornamentation since the Neolithic period.

Field identification & locations

Easily identified by its characteristic translucent to opaque banded patterns and waxy luster. Common worldwide, particularly in regions with historical volcanic activity such as Brazil, India, Germany, and the western United States. Collectors often look for waterlines, fortification banding, and rare color combinations.