Mineral

Limonite with Quartz (Gossan)

Hydrated iron(III) oxide-hydroxide mixture (FeO(OH)·nH2O) with Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (limonite) to 7 (quartz). Color: Yellowish-brown, ochre, dark brown to black. Luster: Dull, earthy, or sub-metallic. Crystal structure: Amorphous to microcrystalline. Cleavage: None.

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

Identified March 30, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (limonite) to 7 (quartz). Color: Yellowish-brown, ochre, dark brown to black. Luster: Dull, earthy, or sub-metallic. Crystal structure: Amorphous to microcrystalline. Cleavage: None.

Formation & geological history

Formed in the oxidation zones (gossans) of iron-rich ore deposits. It is a secondary mineral resulting from the chemical weathering of primary iron minerals like pyrite or hematite, often occurring in various geological ages where moisture is present.

Uses & applications

Historically used as a major iron ore and as a pigment for ochre-colored paints. In modern times, it is used as a colorant in cement and a soil conditioner, while specimens with crystalline associations are kept by collectors.

Geological facts

Limonite is not a true mineral but a 'mineraloid' mixture. It is the primary ingredient in 'Yellow Ochre' used by cave painters over 30,000 years ago. It often forms 'pseudomorphs,' where it replaces the shape of another mineral while keeping its own chemistry.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Often found in wetlands, mine tailings, and weathered outcrops. It is an important indicator for prospectors searching for deeper metal ore veins.