sedimentary
Geode (Calcite or Quartz)
Silicon Dioxide (SiO2) or Calcium Carbonate (CaCO3)
Hardness: 3 (Calcite) to 7 (Quartz); Color: White, cream, or brown; Luster: Vitreous to dull; Crystal structure: Trigonal or Hexagonal; Cleavage: Perfect rhombohedral (if calcite).
- Hardness
- 3 (Calcite) to 7 (Quartz)
- Color
- White, cream, or brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 3 (Calcite) to 7 (Quartz); Color: White, cream, or brown; Luster: Vitreous to dull; Crystal structure: Trigonal or Hexagonal; Cleavage: Perfect rhombohedral (if calcite).
Formation & geological history
Formed as secondary mineral precipitates within cavities (vesicles) of volcanic or sedimentary rocks. Over millions of years, mineral-rich groundwater seeps into these hollows and crystallizes.
Uses & applications
Primarily used as decorative display pieces, for geological education, and in the metaphysical/gemstone collecting market.
Geological facts
The word geode comes from the Greek 'geoides' meaning earth-like. While they look like ordinary rocks on the outside, their interior can contain complex crystal gardens.
Field identification & locations
Identify by its hollow center or rounded, lumpy 'cauliflower' exterior texture. Commonly found in desert regions or areas with limestone/volcanic ash beds.
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