sedimentary

Agate Geode

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Blue-grey, translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Specific gravity: 2.58-2.64.

Hardness: 6
Color: Blue-grey, translucent
Luster: Vitreous to waxy

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Blue-grey, translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Specific gravity: 2.58-2.64.

Formation & geological history

Formed as a secondary deposit in cavities of volcanic rocks or sedimentary formations. Over thousands of years, silica-rich groundwater seeps into these cavities, depositing layers of chalcedony.

Uses & applications

Used primarily for lapidary arts, jewelry, decorative ornaments, and as collector specimens. Historically used for making mortars and pestles due to hardness.

Geological facts

Agate is a variety of chalcedony characterized by its translucency and fine grain. This specimen displays a 'druzy' or solid chalcedony fill within a common host rock matrix.

Field identification & locations

Identified by its waxy luster and conchoidal fracture. Often found in areas with ancient volcanic activity like Brazil, Uruguay, and the Lake Superior region.