sedimentary
Geode (Unopened)
Vug or Geode (primarily Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: Creamy white or tan exterior with possible internal quartz crystals, Luster: Dull/earthy exterior with vitreous interior, Structure: Cryptocrystalline to crystalline, Specific Gravity: 2.6-2.7.
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Creamy white or tan exterior with possible internal quartz crystals, Luster: Dull/earthy exterior with vitreous interior, Structure: Cryptocrystalline to crystalline, Specific Gravity: 2.6-2.7.
Formation & geological history
Formed in sedimentary carbonate environments (like limestone) or volcanic ash. Cavities are created by bubbles or dissolving material, then slowly filled by mineral-rich groundwater over millions of years.
Uses & applications
Primarily used for geological education, lapidary art, home decor, and mineral collecting. When cracked open, they often reveal quartz, chalcedony, or amethyst.
Geological facts
The word geode comes from the Greek word 'Geoides' meaning earth-like. Some geodes are hundreds of millions of years old and can range from an inch to several meters in size.
Field identification & locations
Identify in the field by looking for rounded, cauliflower-like lumpy textures that feel lighter than they look (if hollow). Common in the Keokuk region of the US and Brazil.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary