sedimentary

Geode (Quartz chalcedony variety)

SiO2 (Silicon Dioxide)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: White, translucent, or light grey; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal microcrystalline; Cleavage: None; Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: White, translucent, or light grey
Luster: Vitreous to waxy

Identified May 10, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: White, translucent, or light grey; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal microcrystalline; Cleavage: None; Specific gravity: 2.65

Formation & geological history

Formed through the precipitation of mineral-rich water within hollow cavities of sedimentary or volcanic rocks. Over geological time, cooling or evaporation results in crystal growth inward from the cavity walls.

Uses & applications

Primarily used for geological education, tabletop decor, lapidary art, and popular gemstone collecting.

Geological facts

Geodes are known as 'thunder eggs' in some regions; they appear to be ordinary rocks on the outside but contain hollow centers lined with crystals when cracked open.

Field identification & locations

Identify in the field by their rough, cauliflower-like exterior and unusually light weight for their size (indicating hollow space). Commonly found in desert regions or limestone beds.