sedimentary

Geode (Unopened)

SiO2 (Silicon Dioxide) - Chalcedony/Quartz Geode

Hardness: 6.5-7 (outer shell); Color: Off-white, beige, or dusty tan; Luster: Dull to earthy (outer surface); Crystal structure: Cryptocrystalline/Hexagonal; Cleavage: None; Rounded or cauliflower-like texture.

Hardness: 6
Color: Off-white, beige, or dusty tan
Luster: Dull to earthy (outer surface)

Identified July 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as hollow cavities in volcanic rock or sedimentary bedding (like limestone) that were later filled by mineral-rich hydrothermal fluids or groundwater. These typically range from 30 to 250 million years old.

Uses & applications

Primarily used for collecting, education, and mineral displays. Once cracked open, high-quality specimens are used in lapidary work or home decor.

Geological facts

The word geode comes from the Greek word 'Geoides' which means 'earth-like'. One of the largest geodes ever found, the 'Empress of Uruguay', stands at over 11 feet tall.

Field identification & locations

Identify in the field by looking for rounded, lumpy stones that feel unusually light for their size, suggesting a hollow interior. Commonly found in desert regions or limestone beds in areas like Iowa, Mexico, or Brazil.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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