mineral

Limonite (Iron Ore/Sandstone mixture)

Limonite (FeO(OH)·nH2O) often mixed with Goethite and sedimentary matrix

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous/Microcrystalline; Cleavage: None; Specific Gravity: 2.7–4.3

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull to earthy

Identified March 21, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous/Microcrystalline; Cleavage: None; Specific Gravity: 2.7–4.3

Formation & geological history

Formed through the oxidation and precipitation of iron-rich mineral deposits (like pyrite or magnetite) or as a chemical precipitate in swamps, lakes, and marine environments. This specimen appears and displays heavy weathering typical of iron-rich sedimentary environments.

Uses & applications

Historically used as a common iron ore and as a pigment for yellow and brown ochre. Today, it is mostly a minor iron source or used as a rough material for landscaping and road base in specific regions.

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 tens of thousands of years. It often forms pseudomorphs after other minerals like pyrite.

Field identification & locations

Identify in the field by its distinct yellow-brown streak (even if the rock looks dark), earthy smell when wet, and lack of magnetism. Found globally in iron-rich weathering zones (gossans). Collectors should look for unique botryoidal or stalactitic forms.

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