mineral

Agate (Common Chalcedony)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and translucent white (as seen in-specimen); Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (Trigonal); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Brown, tan, and translucent white (as seen in-specimen)
Luster: Vitreous to waxy

Identified March 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in volcanic rock cavities (vesicles) or sedimentary rock. It deposits from silica-rich groundwater over thousands to millions of years. This specimen appears to be a water-worn river pebble.

Uses & applications

Used primarily in lapidary arts for jewelry, polished pocket stones, and decorative carvings. Industrially used for mortar and pestles due to its hardness and chemical resistance.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered by Greek philosophers. It is a variety of chalcedony that is defined by its translucency and often contains banding, though common 'water agates' like this one may appear solid until light passes through them.

Field identification & locations

Identify in the field by checking for translucency (holding it up to a light source), a waxy texture when wet, and a conchoidal (shell-like) fracture pattern if broken. Commonly found in riverbeds and gravel pits in volcanic regions.