sedimentary
Limonite (Iron Ore)
Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)
Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (does not form distinct crystals); Specific Gravity: 2.7 to 4.3.
- Hardness
- 4 to 5
- Color
- Yellowish-brown to dark brown
- Luster
- Dull to earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (does not form distinct crystals); Specific Gravity: 2.7 to 4.3.
Formation & geological history
Formed from the secondary alteration of other iron minerals through weathering and oxidation in oxidizing environments. It is often found as a precipitate in swamps (bog iron) or as a capping over iron-bearing hydrothermal deposits.
Uses & applications
Historically used as a major source of iron ore; currently used as a pigment (yellow ochre) in dyes and paints and as an additive in cement manufacturing.
Geological facts
Limonite is not a true mineral, but a mixture of related hydrated iron oxide minerals, primarily goethite. It was one of the earliest pigments used by humans, found in prehistoric cave paintings.
Field identification & locations
Identify in the field by its characteristic yellowish-brown streak and earthy appearance. It often appears as a rusty coating on other rocks. Commonly found in gossans (iron hats) and bog deposits globally.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary