mineral

Agate

Agate (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Grey, black, white, and translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Grey, black, white, and translucent
Luster: Waxy to vitreous

Identified June 3, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Grey, black, white, and translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64.

Formation & geological history

Agates form when silica-rich groundwater fills cavities (vugs) in volcanic or sedimentary rocks. The distinctive banding results from rhythmic crystallization over thousands of years. They are commonly found in ancient basalt flows.

Uses & applications

Used extensively in jewelry, ornamental carvings, knife handles, bookends, and high-precision mortar and pestles due to its hardness and chemical resistance.

Geological facts

The word 'Agate' comes from the Achates River in Sicily where they were first discovered. Unlike many minerals, the banding in agate can be incredibly varied, with no two pieces being exactly alike.

Field identification & locations

Identify in the field by looking for a waxy luster on fractured surfaces and distinctive concentric banding inside nodules. Commonly found in riverbeds or areas with weathered volcanic rock like Brazil, Uruguay, or the Lake Superior region.