mineral

Agate

Silicon Dioxide (SiO2) - Chalcedony variety

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored, often with translucent grey, white, and brown banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (Microcrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.60-2.65

Hardness: 6
Luster: Vitreous to waxy

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily within volcanic and metamorphic rocks. It occurs when silica-rich groundwater fills cavities (gas bubbles) in cooling lava or igneous rock, depositing layers of microcrystalline quartz over thousands to millions of years.

Uses & applications

Extremely popular in jewelry as cabochons or pendants, ornamental carvings, knife edges for laboratory balances, and industrial mortars and pestles due to its hardness and resistance to chemicals.

Geological facts

The name 'Agate' comes from the Achates River in Sicily, where it was first discovered in ancient times. It has been used in amulets and hardstone carvings since the Bronze Age, notably in Ancient Greece and Egypt.

Field identification & locations

Identify by its waxy luster, translucency, and characteristic 'concentric' or 'fortification' banding patterns. It is found globally, with notable deposits in Brazil, Uruguay, and the Lake Superior region of the USA. Collectors look for unique patterns like 'moss' or 'fires'.