sedimentary
Mudstone/Siltstone with Liesegang Bands
Argillaceous Sedimentary Rock with Chemical Banding
Hardness: 3-5 (Mohs), Color: Olive-brown to gray with concentric dark banding, Luster: Dull/Earthy, Grain size: Very fine, Crystal structure: Amorphous to microcrystalline.
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Physical properties
Hardness: 3-5 (Mohs), Color: Olive-brown to gray with concentric dark banding, Luster: Dull/Earthy, Grain size: Very fine, Crystal structure: Amorphous to microcrystalline.
Formation & geological history
Formed through the lithification of fine-grained clay or silt particles. The concentric circular patterns are Liesegang rings, produced by the rhythmic precipitation of minerals (usually iron oxides) from groundwater within a porous rock.
Uses & applications
Primarily of interest to collectors and geologists as a study of chemical precipitation. Some variations are used as garden stones or architectural veneer.
Geological facts
The circular rings are often mistaken for fossils or petrified wood, but they are actually a result of chemical diffusion-reaction processes occurring after the rock was deposited.
Field identification & locations
Identify in the field by its fine-grained texture and unique 'bullseye' or swirly dark mineral bands that do not cross-cut the rock but follow internal chemistry. Commonly found in riverbeds or coastal cliffs.
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