sedimentary
Ferruginous Siltstone or Mudstone
Ferruginous Siltstone / Goethitic Sandstone
Hardness 3-5 (variable), brown to reddish-brown color, earthy to dull luster, microcrystalline structure, high iron oxide content, likely rounded by fluvial (water) erosion.
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Physical properties
Hardness 3-5 (variable), brown to reddish-brown color, earthy to dull luster, microcrystalline structure, high iron oxide content, likely rounded by fluvial (water) erosion.
Formation & geological history
Formed through the lithification of silt and clay particles in a low-energy aquatic environment. The dark coloration suggests secondary iron enrichment (mineral staining) during diagenesis or weathering. Often found in Phanerozoic sedimentary basins.
Uses & applications
Primarily of geological interest. Larger deposits of ferruginous rock can serve as iron ore or be crushed for road base and fill material in construction.
Geological facts
Rocks like this with dark, iron-rich patches are often mistaken for meteorites or 'fossilized wood' due to their weight and weathered shape, but they are common earth-bound sedimentary stones.
Field identification & locations
Identify by its weight (denser than regular stones), dull earthy streak, and lack of magnetism (unlike magnetite). Common in creek beds, riverbanks, and areas with exposed sedimentary strata.
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