sedimentary

Sandstone with Dendritic Manganese Oxides

Sandstone (SiO2 predominant) with Oxide Dendrites (MnO2)

Hardness: 6-7 (sandstone matrix), 5-6 (dendrites); Color: Tan/buff matrix with black branching patterns; Luster: Dull/Earthly; Crystal Structure: Clastic matrix with amorphous or microcrystalline growths; Cleavage: None

Hardness: 6-7 (sandstone matrix), 5-6 (dendrites)
Color: Tan/buff matrix with black branching patterns
Luster: Dull/Earthly

Identified June 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of sand particles (usually quartz). The black patterns are manganese or iron-rich mineral solutions that crystallized along bedding planes or fractures in the rock, often resembling fossil plants (pseudofossils).

Uses & applications

Commonly used as flagstone in landscaping, architectural facing, and decorative garden rock. High-quality dendritic specimens are kept by mineral collectors.

Geological facts

These patterns are often mistaken for fossilized ferns or mosses but are actually 'pseudofossils' caused by mineral-rich water seeping through the rock. They grow in a fractal pattern similar to snowflakes or frost on a window.

Field identification & locations

Identify by looking for black, tree-like branch patterns on the surface of flat sedimentary rocks. Common in arid regions like the American Southwest. Collectors should look for vibrant contrast between the matrix and the dendrites.

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