mineral

Agate Geode

Banded Chalcedony (Silicon Dioxide, SiO2) with Quartz crystals

Hardness: 6.5–7 on Mohs scale. Color: Translucent grey, brown, and tan banding. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6.

Hardness: 6
Color: Translucent grey, brown, and tan banding
Luster: Vitreous to waxy

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed in volcanic rock cavities (vesicles) where silica-rich groundwater deposited layers of chalcedony over thousands of years. Often found in basaltic or andesitic lava flows from the Cenozoic era.

Uses & applications

Used primarily as decorative specimens, collectibles, and in metaphysical practices. Polished slabs are used in jewelry (pendants/rings) and coasters.

Geological facts

Every agate geode is unique; no two banding patterns are identical. They are often called 'earth eggs' because of their rough, unassuming exterior compared to their crystalline interior.

Field identification & locations

Identify in the field by looking for rounded, cauliflower-like nodular rocks that feel unusually light for their size. Common in Brazil, Uruguay, and the United States (specifically Oregon and Lake Superior regions).

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