sedimentary

Limonite Concretion

FeO(OH)qnH2O (Hydrated iron(III) oxide-hydroxide mixture)

AI-generated identification · may be incorrect

Hardness: 4-5.5; Color: Yellow-brown, rusty orange, to dark brown; Luster: Earthy, dull, or sub-metallic; Structure: Often amorphous or microcrystalline; Streak: Yellowish-brown.

Hardness: 4-5
Color: Yellow-brown, rusty orange, to dark brown
Luster: Earthy, dull, or sub-metallic

Identified July 11, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5; Color: Yellow-brown, rusty orange, to dark brown; Luster: Earthy, dull, or sub-metallic; Structure: Often amorphous or microcrystalline; Streak: Yellowish-brown.

Formation & geological history

Formed through the chemical weathering of iron-rich minerals (like pyrite or magnetite) or precipitation from iron-saturated groundwater in sedimentary environments. Common in bog deposits and weathered soil layers.

Uses & applications

Historically used as a low-grade iron ore and as a pigment for ochre paint. Primarily of interest to collectors and geologists as a secondary mineral specimen.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It is responsible for the yellowish-brown coloring in many soils and desert varnishes.

Field identification & locations

Identify by its characteristic yellowish-brown streak, earthy appearance, and tendency to occur as small nodules or crusts. Common in rusty sand deposits or near oxidizing iron sources.