sedimentary
Geode Nodules / Chert Pebble
Silicon Dioxide (SiO2) / Quartz concretion
Hardness: 6.5-7 on Mohs scale; Color: Dull brown, tan, gray exterior; Luster: Earthy to dull exterior; Structure: Spherical to ovoid concretion, potentially hollow or crystal-lined inside.
- Hardness
- 6
- Color
- Dull brown, tan, gray exterior
- Luster
- Earthy to dull exterior
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Dull brown, tan, gray exterior; Luster: Earthy to dull exterior; Structure: Spherical to ovoid concretion, potentially hollow or crystal-lined inside.
Formation & geological history
Formed in sedimentary rocks such as limestone or shale through chemical precipitation around a core nucleus, or as hollow cavities filled with silica-rich water over time.
Uses & applications
Used primarily for rock collecting, lapidary arts, education, and decorative displays when cracked open to reveal internal crystals.
Geological facts
Geode nodules often look like completely ordinary, rough round rocks on the outside, but can contain sparkling quartz, chalcedony, or amethyst crystals inside.
Field identification & locations
Identify by its rounded, spherical nodular shape and relative lightness compared to solid rock of similar size. Commonly found in stream beds, gravel deposits, and limestone formations.
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