sedimentary

Dendritic Siltstone

Siltstone with Manganese Oxide dendrites (MnO2)

AI-generated identification · may be incorrect

Hardness: 3–4 (Mohs); Color: Light grey to beige with dark brown/black tree-like patterns; Luster: Dull/Earthy; Structure: Clastic; Cleavage: None (fractures into plates); Specific Gravity: 2.6

Hardness: 3–4 (Mohs)
Color: Light grey to beige with dark brown/black tree-like patterns
Luster: Dull/Earthy

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 3–4 (Mohs); Color: Light grey to beige with dark brown/black tree-like patterns; Luster: Dull/Earthy; Structure: Clastic; Cleavage: None (fractures into plates); Specific Gravity: 2.6

Formation & geological history

Formed from the lithification of silt-sized particles in low-energy aquatic environments. The dark patterns are manganese-rich mineral solutions that crystallized in fractures over millions of years.

Uses & applications

Primarily used as a decorative stone, in lapidary work for cabochons, and as an educational tool to demonstrate pseudo-fossils.

Geological facts

The tree-like patterns are often mistaken for fossilized ferns or plants, but they are purely inorganic crystal growths called dendrites.

Field identification & locations

Identifiable by the flat, plate-like breakage of the siltstone matrix and the branching fractal patterns. Common in Utah and Germany. Collectors should look for high contrast patterns.