mineral

Agate

Silicon Dioxide (SiO2) - Chalcedony

Hardness: 6.5-7 on Mohs scale; Color: Translucent to opaque with banding in shades of white, cream, yellow, orange, brown, and grey; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.58-2.64

Hardness: 6
Luster: Waxy to vitreous

Identified July 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed within gas cavities or voids in volcanic rocks (such as basalt) or certain sedimentary rocks through the low-temperature deposition of silica from groundwater containing dissolved quartz. Bands reflect sequential deposition phases.

Uses & applications

Used extensively as an ornamental stone, lapidary arts, jewelry (cabochons, beads), decorative carvings, and historically for mortar and pestle sets due to its hardness and chemical resistance.

Geological facts

Agate is named after the Achates River (now the Dirillo River) in Sicily, where ancient Greek philosophers first discovered it. Unique patterns occur due to trace iron, manganese, or other mineral inclusions during silica deposition.

Field identification & locations

Identify in the field by its waxy luster, hardness (scratches steel), conchoidal fracture, and characteristic concentric or parallel banding when light passes through translucent sections. Commonly found in basaltic gravel beds, river sediments, and volcanic regions worldwide (e.g., Lake Superior region, Brazil, Uruguay, Madagascar).