sedimentary
Sandstone Geode
Sedimentary Geode (Silica/Calcite composition)
Hardness: 6-7 (exterior shell), Color: Tan, beige, earthy brown, Luster: Dull/Earthy (exterior), Crystal structure: Cryptocrystalline to crystalline interior, Cleavage: None
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Physical properties
Hardness: 6-7 (exterior shell), Color: Tan, beige, earthy brown, Luster: Dull/Earthy (exterior), Crystal structure: Cryptocrystalline to crystalline interior, Cleavage: None
Formation & geological history
Formed in sedimentary rock layers where a cavity (often from a fossil or bubble) was filled over millions of years by mineral-rich groundwater precipitating silica or calcite.
Uses & applications
Geological study, lapidary use (cutting and polishing), and popular for children and hobbyists to crack open.
Geological facts
While the outside looks like a common rock, the round, lumpy texture often indicates a hollow center lined with crystals. These are frequently found in limestone and shale beds.
Field identification & locations
Identify by its rounded, nodular shape and light weight relative to its size (if hollow). Common in the Midwestern United States and Morocco.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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