sedimentary

Geode (unopened)

Quartz-filled Geode (SiO2)

Hardness: 7 (Mohs scale) for interior quartz. Color: Tan, beige, or grey exterior; white to gray interior. Luster: Dull/earthy exterior; vitreous interior. Crystal structure: Cryptocrystalline or macrocrystalline quartz. Specific gravity: Approx 2.65.

Hardness: 7 (Mohs scale) for interior quartz
Color: Tan, beige, or grey exterior
Luster: Dull/earthy exterior

Identified June 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary rock layers (often limestone or shale) via the deposition of minerals from hydrothermal fluids or groundwater into hollow cavities. These typically date from the Paleozoic to Cenozoic eras.

Uses & applications

Primarily used for geological collecting, home decor, and educational purposes. Historically used as a source for quartz or chalcedony.

Geological facts

Geodes are often mistaken for common field stones until they are cracked open to reveal a hollow center filled with crystals. The word 'geode' comes from the Greek 'geoides,' meaning 'earth-like.'

Field identification & locations

Identified by its spherical or sub-spherical shape, relatively low weight for its size (indicating a hollow center), and bumpy 'cauliflower' texture. Commonly found in riverbeds and limestone outcrops in the Midwestern United States and Brazil.