sedimentary
Geode (Quartz chalcedony variety)
SiO2 (Silicon Dioxide)
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
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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.
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