sedimentary

Limonite on Sandstone

Iron Oxyhydroxide (FeO(OH)·nH2O) on Quartz Sandstone

AI-generated identification · may be incorrect

Hardness: 4-5.5 (limonite) and 7 (sandstone); Color: Yellow-ochre to brownish-yellow streaks; Luster: Dull, earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Grained texture.

Hardness: 4-5
Color: Yellow-ochre to brownish-yellow streaks
Luster: Dull, earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5 (limonite) and 7 (sandstone); Color: Yellow-ochre to brownish-yellow streaks; Luster: Dull, earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Grained texture.

Formation & geological history

Formed via the chemical weathering of iron-rich minerals such as pyrite or magnetite within sedimentary layers. The limonite precipitates as a secondary mineral coating sandstone grains or filling pore spaces.

Uses & applications

Historically used as a yellow ochre pigment for paints; also an ore of iron. Sandstone is widely used in construction and landscaping.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, primarily goethite. It was the source of some of the earliest pigments used by humans for cave paintings.

Field identification & locations

Identify by the characteristic ochre-yellow streak it leaves on unglazed porcelain. Commonly found in oxidized zones of mineral deposits and in sedimentary basins where groundwater flow is prevalent.