sedimentary
Goethite / Limonite Gossan
Hydrated Iron Oxide (FeO(OH))
Hardness: 5-5.5; Color: Dark brown to black with yellowish-orange patches; Luster: Submetallic to dull; Crystal structure: Orthorhombic (usually massive/earthy); Specific gravity: 3.3-4.3
- Hardness
- 5-5
- Color
- Dark brown to black with yellowish-orange patches
- Luster
- Submetallic to dull
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Physical properties
Hardness: 5-5.5; Color: Dark brown to black with yellowish-orange patches; Luster: Submetallic to dull; Crystal structure: Orthorhombic (usually massive/earthy); Specific gravity: 3.3-4.3
Formation & geological history
Formed by the oxidation and weathering of primary iron-bearing sulfide minerals in the upper part of an ore deposit, creating a 'iron hat' or gossan.
Uses & applications
Historically used as an iron ore; currently used as a pigment (ochre), a collector specimen, and a geological indicator for underlying metal deposits.
Geological facts
Gossans were used by early prospectors as 'signposts' for valuable gold and copper deposits hidden deep underground. Limonite is not a single mineral but a mixture of hydrated iron oxides.
Field identification & locations
Identified by its rusty color, heavy weight compared to surrounding rocks, and porous, boxwork texture. Common in arid, weathered mining districts.
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