mineral
Limonite (Iron Ore)
FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)
Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (often found in botryoidal or earthy masses); Specific Gravity: 2.7-4.3
- Hardness
- 4
- Color
- Yellowish-brown to dark brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (often found in botryoidal or earthy masses); Specific Gravity: 2.7-4.3
Formation & geological history
Formed by the oxidation and hydration of iron-rich mineral sulfides (like pyrite) through weathering and secondary precipitation in sedimentary or metamorphic environments.
Uses & applications
Historically used as a major source of iron ore; remains important as an earth pigment (ochre) for paints and dyes.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was the source of yellow ochre used by prehistoric humans in cave paintings.
Field identification & locations
Identified by its signature yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Commonly found in gossans (weathered tops of ore deposits) and marshy areas as 'bog iron'.
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Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Sandstone with Mineral Veining or Crust
Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock