sedimentary
Geode (Unopened)
Silicon Dioxide (SiO2) in sedimentary vugs
Hardness: 7 (Mohs scale), Color: Dirty white/brown exterior with possible quartz inside, Luster: Dull/earthy exterior, Crystal structure: Amorphous/microcrystalline exterior, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dirty white/brown exterior with possible quartz inside, Luster: Dull/earthy exterior, Crystal structure: Amorphous/microcrystalline exterior, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed by precipitation of minerals from hydrothermal fluids or groundwater into hollow cavities within sedimentary or volcanic rock. Often found in limestone or shale beds.
Uses & applications
Primarily used as decorative display pieces, for geological education, and by mineral collectors. When cracked open, the inside crystals may be used in jewelry.
Geological facts
Geodes are known as 'treasure chests' of the earth. Until they are broken open, it is impossible to know if they contain clear quartz, purple amethyst, or are hollow/solid clusters of minerals.
Field identification & locations
Identify in the field by their rounded, nodular shape which differs from the surrounding bedrock; they often feel lighter than they look if they are hollow. Common in desert environments or limestone quarries.
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