mineral

Agate (Chalcedony)

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Translucent brownish-grey with iron inclusions; Luster: Waxy to vitreous; Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Translucent brownish-grey with iron inclusions
Luster: Waxy to vitreous

Identified June 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in the cavities of igneous rocks, particularly volcanic lavas. These processes can take millions of years, often dating back to the Cenozoic or Mesozoic eras.

Uses & applications

Used primarily in lapidary arts for cabochons, beads, and carvings. Historically used for making mortars and pestles due to hardness, and extensively in jewelry and decorative ornaments.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. The brownish spots in this specimen are likely iron or manganese oxide inclusions known as dendrites or 'moss' depending on their shape.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. Frequently found in riverbeds, volcanic ash beds, or desert environments. Common in Brazil, India, and the Western USA.