mineral

Limonite / Goethite (Ironstone Nodule)

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5 on Mohs scale. Color: Dark brown, black, to yellowish-brown. Luster: Earthy, sub-metallic, to dull. Crystal Structure: Amorphous or microcrystalline aggregate. Streak: Yellowish-brown.

Hardness: 4-5
Color: Dark brown, black, to yellowish-brown
Luster: Earthy, sub-metallic, to dull

Identified July 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the weathering and oxidation of iron-rich minerals like pyrite, siderite, or magnetite in sedimentary environments or soil zones. Often forms crusts, concretions, or pseudomorphs.

Uses & applications

Historically used as a minor iron ore and as a natural brown/yellow pigment (ochre). Collected by mineral enthusiasts.

Geological facts

Limonite is not a true single mineral, but a field term for a mixture of hydrated iron oxide minerals, predominantly goethite along with lepidocrocite and jarosite.

Field identification & locations

Identified by its heavy weight for its size, rusty/dark coloration, and characteristic yellowish-brown streak on unglazed porcelain. Common in sedimentary rock beds and soil surfaces worldwide.