mineral

Agate Geode

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, white, and translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Gray, white, and translucent
Luster: Vitreous to waxy

Identified May 3, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, white, and translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed in cavities or vesicles of volcanic rock (basalt) or sedimentary rock. Silica-rich fluids percolate into these voids, depositing layers of chalcedony over millions of years starting from the Eocene to recent epochs.

Uses & applications

Polished specimens are used for home decor, jewelry cabochons, metaphysical practices, and as collectibles. Industrially, high-quality chalcedony can be used for precision mortars and pestles.

Geological facts

This specimen features a 'water-line' or horizontal agate banding, indicating the orientation of the geode while it was forming. Agates are the state rock of several US states including Minnesota and South Dakota.

Field identification & locations

Identify in the field by looking for rounded nodules with a rough, 'cauliflower-like' exterior in volcanic ash beds or gravel deposits. Common in Brazil, Uruguay, and the western United States.