sedimentary

Limonite (Iron Bog Ore)

FeO(OH)nH2O

Hardness: 4-5.5; Color: Yellow-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous/Microcrystalline; Streak: Yellowish-brown; Specific Gravity: 2.7–4.3

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

Identified July 8, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5; Color: Yellow-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous/Microcrystalline; Streak: Yellowish-brown; Specific Gravity: 2.7–4.3

Formation & geological history

Forms as a secondary material through the oxidation of iron-rich mineral ores like pyrite, or through precipitation in bogs, springs, and marine environments.

Uses & applications

Primary source of iron ore historically; used today as a natural earth pigment (ochre) and as a low-grade iron source.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It was the original source of yellow ochre used in cave paintings over 15,000 years ago.

Field identification & locations

Identify by its distinctive yellowish-brown streak on a porcelain plate and its rusty, earthy appearance. Often found in swampy areas or gossans above sulfide deposits.