sedimentary

Limonitic Iron Ore / Goethite

Hydrated Iron(III) oxide-hydroxide (primarily FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5 (Mohs); Color: Dark brown to yellow-ochre; Luster: Submetallic, dull, or earthy; Crystal Structure: Orthorhombic (if crystalline); Cleavage: Perfect (if individual crystals); Specific Gravity: 2.7-4.3

Hardness: 4
Color: Dark brown to yellow-ochre
Luster: Submetallic, dull, or earthy

Identified April 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical weathering of iron-rich minerals such as pyrite, magnetite, and siderite in oxidation zones. It often occurs as a secondary mineral in sedimentary bog iron deposits or gossans over sulfide ore bodies.

Uses & applications

Historically a major source of iron ore. Today, it is used as a natural earth pigment (yellow ochre) in paints, an iron supplement in fertilizers, and occasionally as a low-value collector specimen.

Geological facts

Limonite is not a true mineral but a 'mineraloid' mixture of hydrated iron oxides. It was a primary source of iron for ancient civilizations and is the substance responsible for the yellow and brown colors in many soils and sedimentary rocks.

Field identification & locations

Identify in the field by its distinct yellow-brown 'ochre' streak when rubbed against unglazed porcelain. It is commonly found in weathered rock outcrops, swamps (bog iron), and as a coating on other stones in mining districts.