mineral

Limonite (with Goethite/Ironstone)

FeO(OH)·nH2O (Hydrated Iron Oxide)

Hardness: 4-5.5 on Mohs scale; Color: Dull yellow-brown to bright orange; Luster: Earthy to dull; Crystal structure: Amorphous (no visible crystals); Cleavage: None; Specific gravity: 2.7–4.3

Hardness: 4-5
Color: Dull yellow-brown to bright orange
Luster: Earthy to dull

Identified March 18, 2026More mineral →

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Physical properties

Hardness: 4-5.5 on Mohs scale; Color: Dull yellow-brown to bright orange; Luster: Earthy to dull; Crystal structure: Amorphous (no visible crystals); Cleavage: None; Specific gravity: 2.7–4.3

Formation & geological history

Formed through the secondary oxidation and chemical weathering of iron-rich mineral deposits (like pyrite or magnetite) in swampy, sedimentary, or hydrothermal environments. Often geological age ranges from recent to hundreds of millions of years.

Uses & applications

Historically used as an iron ore; currently used as a pigment (ochre) for paints and dyes. In industry, it is used for chemical processes and occasionally as a low-grade construction fill.

Geological facts

Limonite is the primary source of 'yellow ochre' used by early humans for cave paintings. It is also a common component of 'bog iron' found in wetlands. It isn't a true mineral but a mixture of hydrated iron oxides.

Field identification & locations

Identify by its distinctive yellow-orange-brown streak (scratched on porcelain) and earthy texture. Often found near rusted iron pipes or in iron-rich sedimentary bands. Collectors look for botryoidal (grape-like) shapes.

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