sedimentary

Sandstone with Manganese Oxide Patina

Clastic Sedimentary Rock (primarily SiO2)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale), Color: tan/buff interior with black exterior coating, Luster: dull/earthy, Crystal structure: granular clastic texture, Cleavage: none, Specific gravity: 2.2-2.8

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs scale), Color: tan/buff interior with black exterior coating, Luster: dull/earthy, Crystal structure: granular clastic texture, Cleavage: none, Specific gravity: 2.2-2.8

Formation & geological history

Formed from the accumulation and cementation of sand-sized mineral grains or rock fragments. The dark exterior is a 'desert varnish' or manganese/iron oxide coating formed by slow mineral precipitation over long periods in arid or semi-arid environments.

Uses & applications

Common building material, aggregate in construction, and occasionally used in landscaping. This specific weathered specimen is mainly of interest for geological study or amateur collecting.

Geological facts

The dark coating, often called desert varnish, can take thousands of years to form and is often composed of clay minerals combined with iron and manganese oxides concentrated by microbial activity.

Field identification & locations

Identify in the field by the grainy, sandpaper-like feel of the interior and the thin, dark weathering rind on the surface. Commonly found in riverbeds, deserts, and mountain outcrops. Collectors look for unique weathering patterns and shapes.