mineral
Limonite-stained ironstone, possibly goethite
Goethite/limonite (FeO(OH) and hydrated iron oxides), identification tentative
AI-generated identification · may be incorrectDark brown to black, earthy-to-submetallic luster with rusty yellow-brown coatings; hardness about 4–5.5 Mohs, opaque, irregular fracture, and no obvious cleavage. The specimen appears dense and iron-rich, though a photo cannot confirm composition.
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Physical properties
Dark brown to black, earthy-to-submetallic luster with rusty yellow-brown coatings; hardness about 4–5.5 Mohs, opaque, irregular fracture, and no obvious cleavage. The specimen appears dense and iron-rich, though a photo cannot confirm composition.
Formation & geological history
Forms by oxidation and weathering of iron-bearing minerals, commonly as a replacement or cavity coating in soils, veins, and altered rocks; formation may range from recent weathering to ancient deposits.
Uses & applications
Used as an iron ore and historically as a brown-yellow pigment; attractive pieces are collected but are generally not gem material.
Geological facts
Goethite commonly develops botryoidal, fibrous, or stalactitic forms, while “limonite” is a field term for poorly crystalline hydrated iron oxides rather than a single mineral.
Field identification & locations
Look for a rusty streak, high density, opaque brown-black color, and association with weathered iron minerals; a streak test and hardness test help distinguish it from hematite, magnetite, and sulfides. Common worldwide, especially in laterites, gossans, and oxidized ore zones.
