mineral

Agate Geode

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored bands (grey, white, brown) with a crystalline center; Luster: Vitreous to waxy; Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Luster: Vitreous to waxy

Identified January 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed within cavities in igneous rocks (basalt) or sedimentary rocks when silica-rich groundwater precipitates layers of microscopic quartz crystals over millions of years. This specimen shows classic druzy quartz formation in the center.

Uses & applications

Extensively used in lapidary arts, jewelry (cabochons), interior decor, and as collectible museum specimens. Historically used for making mortars and pestles due to its hardness.

Geological facts

The banding in agates is caused by periodic changes in the concentration and composition of the silica-bearing fluids during deposition. Some geodes can contain liquid inclusions preserved for millions of years.

Field identification & locations

Identified by the distinct white/translucent banding (chalcedony) surrounding a hollow or crystal-filled center. Commonly found in Brazil, Uruguay, and the Lake Superior region. In the field, look for lumpy, rounded nodules with a weathered exterior that feels unusually light for their size.