sedimentary
Quartz Geode (Cracked)
Quartz (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Clear to milky white crystals often covered by a brown or gray exterior crust; Luster: Vitreous (glassy) inside, dull outside; Crystal Structure: Hexagonal; Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous (glassy) inside, dull outside
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Physical properties
Hardness: 7 on Mohs scale; Color: Clear to milky white crystals often covered by a brown or gray exterior crust; Luster: Vitreous (glassy) inside, dull outside; Crystal Structure: Hexagonal; Specific Gravity: 2.65
Formation & geological history
Formed in cavities (vugs) within sedimentary or volcanic rocks. Mineral-rich groundwater seeps into the hollow spaces, depositing microcrystalline and then macrocrystalline quartz over thousands to millions of years.
Uses & applications
Commonly used for geological education, home decor, and as entry-level mineral specimens for collectors. Quartz itself is used in electronics and glass-making.
Geological facts
Geodes are often called 'thunder eggs' when they are solid or have a specific volcanic origin. The word geode comes from the Greek word 'Geoides' which means 'earth-like'.
Field identification & locations
Identify in the field by looking for rounded, bumpy, potato-like stones that feel lighter than they look (if hollow). Found in stream beds, deserts, and limestone quarries.
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