mineral

Limonite or Goethite (Ironstone)

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

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs), Color: Dark brown to earthy yellow/orange, Luster: Submetallic to earthy, Crystal Structure: Amorphous or microcrystalline, Cleavage: None

Hardness: 4-5

Identified July 20, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs), Color: Dark brown to earthy yellow/orange, Luster: Submetallic to earthy, Crystal Structure: Amorphous or microcrystalline, Cleavage: None

Formation & geological history

Formed as secondary mineral species through the oxidation and weathering of primary iron-bearing minerals (like pyrite or magnetite) in sedimentary or metamorphic settings.

Uses & applications

Historically used as an iron ore and as a source for yellow and brown ochre pigments. In modern times, it is a minor ore of iron and a specimen for collectors.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxides, primarily goethite. It was the primary source of iron for many early human civilizations due to its abundance near the surface.

Field identification & locations

Identified by its signature yellowish-brown streak on a porcelain plate and its rusty appearance. Often found in wetlands (bog iron) or as a weathering crust on iron-rich rocks.