mineral

Agate Geode

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Banded grey, brown, and white with a clear/white crystalline interior; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64

Hardness: 6
Luster: Vitreous to waxy

Identified July 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed by the deposition of silica-rich fluids within gas bubbles or cavities in volcanic lava or sedimentary rocks. Over millions of years, multiple layers of chalcedony form the rind, often leaving a hollow space lined with quartz crystals.

Uses & applications

Used extensively in jewelry (cabochons), interior decor, or as specimens for educational and metaphysical collections. Smaller geodes are often sold as 'break-your-own' kits.

Geological facts

The banding in the agate walls is caused by changes in the chemical composition of the silica fluids during formation. The name 'Agate' originates from the Achates River in Sicily where these stones were first found in antiquity.

Field identification & locations

Identified in the field by their rough, cauliflower-like exterior texture and round or oval shape. They feel heavier than regular rocks due to the solid quartz lining. Often found in dry river beds and volcanic regions like those in Brazil, Mexico, or the United States (Oregon/Utah).