sedimentary

Sandstone with Manganese Dendrites/Oxide coatings

Arenite with Pyrolusite and Romanechite (MnO2)

AI-generated identification · may be incorrect

Hardness: 6-7 (sandstone matrix), 5-6 (oxide patches). Color: Tan/brown base with black or metallic dark grey splotches. Luster: Earthy, dull, or sub-metallic on the dark parts. Structure: Granular/Clastic.

Hardness: 6-7 (sandstone matrix), 5-6 (oxide patches)
Color: Tan/brown base with black or metallic dark grey splotches
Luster: Earthy, dull, or sub-metallic on the dark parts

Identified April 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation and cementation of sand-sized grains, often in riverbeds, deserts, or marine environments. The dark minerals are secondary deposits formed by the precipitation of manganese-rich groundwater through the porous stone over thousands of years.

Uses & applications

Common sandstone is used in construction and paving. Specimens with aesthetic manganese patterns are prized by mineral collectors and used in educational rock kits.

Geological facts

Manganese oxides often form 'pseudofossils' called dendrites that look like ferns or trees, though they are purely mineral growths. This specimen shows a thick surface coating of these oxides.

Field identification & locations

Identify in the field by the grainy feel of the tan matrix (sand) and dark stains that don't rub off like soot. Commonly found in outcroppings of sedimentary basins worldwide.