sedimentary
Quartz Geode
Silicon Dioxide (SiO2) in Geodic cavity
Hardness: 7 on Mohs scale. Color: White to colorless crystals inside a tan/yellowish host rock. Luster: Vitreous (glassy) crystals. Crystal Structure: Hexagonal. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- White to colorless crystals inside a tan/yellowish host rock
- Luster
- Vitreous (glassy) crystals
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Physical properties
Hardness: 7 on Mohs scale. Color: White to colorless crystals inside a tan/yellowish host rock. Luster: Vitreous (glassy) crystals. Crystal Structure: Hexagonal. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed in sedimentary or volcanic rock cavities. Mineral-rich groundwater seeps into these hollow spaces, depositing layers of silica that slowly crystallize over millions of years. This process typically occurs in desert environments or limestone beds.
Uses & applications
Used primarily for educational purposes, home decor, geological collecting, and lapidary work. Small, common geodes are often used in children's 'break-your-own' kits.
Geological facts
The word 'geode' comes from the Greek word 'Geoides' meaning 'earth-like'. While they look like plain rocks on the outside, they contain hollow centers filled with sparkling crystals. Large geodes can contain huge amethyst cathedrals.
Field identification & locations
Identify in the field by looking for rounded, bumpy 'nodules' that feel lighter than expected for their size. Commonly found in Morocco, Brazil, Mexico, and the U.S. states of Iowa, Indiana, and Kentucky.
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