sedimentary

Geode (Unopened)

Silicon Dioxide (SiO2) in sedimentary host rock

AI-generated identification · may be incorrect

Hardness: 7 (Quartz interior), 5-6 (outer rind). Color: Tan, beige, or grey exterior. Luster: Dull/earthy exterior. Crystal Structure: Trigonal/Amorphous. Specific Gravity: 2.6-2.7.

Hardness: 7 (Quartz interior), 5-6 (outer rind)
Color: Tan, beige, or grey exterior
Luster: Dull/earthy exterior

Identified June 20, 2026More sedimentary →

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Physical properties

Hardness: 7 (Quartz interior), 5-6 (outer rind). Color: Tan, beige, or grey exterior. Luster: Dull/earthy exterior. Crystal Structure: Trigonal/Amorphous. Specific Gravity: 2.6-2.7.

Formation & geological history

Formed in sedimentary rock cavities (such as limestone or shale) through mineral precipitation from hydrothermal fluids or groundwater over millions of years. Common in Mississippian and Devonian strata.

Uses & applications

Primarily used for lapidary work, educational displays, and as a popular item for amateur rock collectors and hobbyists.

Geological facts

The word geode comes from the Greek word 'Geoides' which means earth-like. They look like ordinary rocks on the outside, but can contain spectacular hollow cavities lined with crystals like quartz, amethyst, or calcite.

Field identification & locations

Identify by its unusually light weight (if hollow) and rounded, bumpy, 'cauliflower-like' exterior texture. Commonly found in riverbeds and limestone outcrops in the Midwest USA (Keokuk region) and Brazil.