mineral

Limonite (Ironstone)

Limonite (mixture of hydrated iron oxides, primarily Goethite α-FeO(OH))

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy, or sub-metallic when wet; Crystal Structure: Amorphous/Microcrystalline; Streak: Yellow-brown.

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull, earthy, or sub-metallic when wet

Identified April 12, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy, or sub-metallic when wet; Crystal Structure: Amorphous/Microcrystalline; Streak: Yellow-brown.

Formation & geological history

Formed as a secondary material through the oxidation and weathering of primary iron-bearing minerals (like pyrite or magnetite) in sedimentary environments or as bog deposits.

Uses & applications

Historically used as an iron ore and a pigment (brown ochre). It is still used today as a natural colorant in paints and concrete.

Geological facts

Limonite is not a true mineral but a mineraloid. It was one of the earliest pigments used by humans, found in cave paintings dating back thousands of years.

Field identification & locations

Identify in the field by its distinct yellow-brown 'ochre' streak on a porcelain plate and its high density compared to common silicate rocks. It often has a crust-like or botryoidal texture.

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