sedimentary

Yellow Ocherous Siltstone (Limonitic Shale)

Limonitic Siltstone / Goethite-rich Sedimentary Rock

Hardness: 2-4 (Mohs scale); Color: Yellow to brownish-orange; Luster: Dull, earthy; Crystal structure: Microcrystalline/Amorphous; Cleavage: None (conchoidal or irregular fracture); Specific gravity: 2.7-4.3 influenced by iron content

Hardness: 2-4 (Mohs scale)
Color: Yellow to brownish-orange
Luster: Dull, earthy

Identified June 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of fine-grained silt and clay in low-energy environments like lake beds or floodplains, followed by the secondary oxidation and hydration of iron minerals (limonitization) within the sedimentary layers.

Uses & applications

Historically used as a natural pigment (yellow ochre) for paints and dyes. Modern uses include clay manufacturing, land fill, and as a minor source of low-grade iron ore.

Geological facts

Rocks colored by limonite have been used as cave painting pigments since the Paleolithic period. The distinct yellow-orange color is often due to the oxidation of pyrite or other iron-bearing minerals localized in the sediment.

Field identification & locations

Identify by its earthy texture and mustard-yellow streak. It is commonly found in sedimentary basins and alongside weathered iron deposits. Collectors look for pieces with distinct layers or fossils.

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