sedimentary
Chert Geode Nodules
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, or white exterior with possible crystalline interior. Luster: dull to waxy. Structure: nodular/spherical. Cleavage: none (conchoidal fracture).
- Luster
- dull to waxy
Identified More sedimentary →
Explore Chert Geode Nodules in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, or white exterior with possible crystalline interior. Luster: dull to waxy. Structure: nodular/spherical. Cleavage: none (conchoidal fracture).
Formation & geological history
Formed via chemical precipitation of silica-rich fluids within cavities of sedimentary rocks like limestone or dolomite, often during diagenesis.
Uses & applications
Primarily collected by rockhounds as lapidary material; larger specimens may be cracked open to reveal crystals. Historically used for stone tools due to its hardness.
Geological facts
Geodes are often indistinguishable from ordinary stones on the outside. The only way to know if they are hollow or contain crystals is to break them or saw them in half.
Field identification & locations
Found in riverbeds, limestone quarries, and desert environments. Identify by their rounded, lumpy, or cauliflower-like exterior texture and high density compared to similar-looking rocks.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary