sedimentary

Geode or Concretion

Silica-filled nodule (likely SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (if quartz/agate center); Color: Dull brownish-gray exterior, potential crystalline interior; Luster: Earthy exterior; Crystal system: Trigonal (if quartz); Cleavage: None.

Hardness: 6
Color: Dull brownish-gray exterior, potential crystalline interior
Luster: Earthy exterior

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (if quartz/agate center); Color: Dull brownish-gray exterior, potential crystalline interior; Luster: Earthy exterior; Crystal system: Trigonal (if quartz); Cleavage: None.

Formation & geological history

Formed in sedimentary rock cavities (such as limestone) or volcanic ash beds through groundwater mineral precipitation over millions of years.

Uses & applications

Primarily used as lapidary material, decorative display pieces, or for education/collecting once sliced or cracked open.

Geological facts

Until opened, it is often impossible to know if a geode contains beautiful crystals or is solid (a nodule/thunder egg).

Field identification & locations

Identify by a rounded, bumpy, 'cauliflower' exterior texture that feels lighter than a normal rock of its size. Common in the American Midwest and desert regions.