mineral
Limonite / Goethite Ironstone Concretion
FeO(OH)·nH2O (Hydrated Iron Oxide)
Hardness: 4 to 5.5 on Mohs scale. Color: Dark reddish-brown, yellowish-brown, blackish-brown. Luster: Metallic to dull, sub-metallic, earthy. Specific Gravity: 2.7 to 4.3. Crystal System: Amorphous or microcrystalline (frequently pseudomorphic). Cleavage: None.…
- Hardness
- 4 to 5
- Color
- Dark reddish-brown, yellowish-brown, blackish-brown
- Luster
- Metallic to dull, sub-metallic, earthy
Identified More mineral →
Explore Limonite / Goethite Ironstone Concretion in the encyclopedia →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: Dark reddish-brown, yellowish-brown, blackish-brown. Luster: Metallic to dull, sub-metallic, earthy. Specific Gravity: 2.7 to 4.3. Crystal System: Amorphous or microcrystalline (frequently pseudomorphic). Cleavage: None. Feature: Porous, pitted surface with hollow cavities, often weakly or non-magnetic.
Formation & geological history
Formed as a secondary mineral product through the oxidation and weathering of primary iron-rich minerals (such as pyrite, marcasite, or siderite) in sedimentary or soil environments. Moisture and oxygen leach iron, forming hollowed, crusty oxide concretions or ironstone nodules over thousands to millions of years.
Uses & applications
Historically used as a major ore of iron and a natural yellow/brown pigment (ochre). Collected by amateur rockhounds and used in lapidary work or landscape features when found in larger sizes.
Geological facts
These hollow or pitted nodules are often mistaken for iron meteorites due to their heavy weight and dark metallic crust. However, they lack the fusion crust, widmanstätten patterns, and high nickel content of genuine meteorites. The interior cavity sometimes contains loose sand or clay, producing a 'rattle stone' or aetite.
Field identification & locations
Identify in the field by its distinct reddish-brown streak, heavy feeling (density), rusty orange-brown cavities, and lack of strong magnetism compared to pure magnetite. Commonly found in stream beds, soil zones overlying iron formations, and weathered sedimentary sandstone/shale deposits worldwide.
More like this
Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Limonite / Goethite (Iron Ore Mineral nodule)
FeO(OH)·nH2O / FeO(OH)
mineral
Schist
Schist
Metamorphic
Septarian Pebble
Septarian nodule / Concretion
sedimentary
Potassium Feldspar (Orthoclase)
Orthoclase (KAlSi3O8)
mineral
Sandstone with Mineral Veining or Crust
Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)
sedimentary