mineral

Agate Geode (Unopened)

Cryptocrystalline Quartz (SiO2) with Chalcedony

Hardness: 6.5-7 (Mohs scale); Color: Brownish-tan exterior (concretion), potentially white/purple/blue interior; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None/Conchoidal.

Hardness: 6
Luster: Waxy to vitreous

Identified June 14, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brownish-tan exterior (concretion), potentially white/purple/blue interior; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None/Conchoidal.

Formation & geological history

Formed within cavities of volcanic or sedimentary rocks through the slow precipitation of silica-rich groundwater. Often found in riverbeds or areas with volcanic history, ranging from millions to billions of years old.

Uses & applications

Used in jewelry, decorative arts, lapidary projects, and as a popular collector's specimen for rockhounds.

Geological facts

The word geode comes from the Greek word 'geōdēs' meaning 'earthlike.' Many unopened geodes contain hollow centers lined with quartz crystals or solid bands of agate.

Field identification & locations

Identify by its cauliflower-like bumpy exterior and relatively light weight compared to its size if hollow. Commonly found in Brazil, Uruguay, and the Midwestern United States.

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