sedimentary
Ironstone concretion
Siderite or Limonite concretion (FeCO3 or FeO(OH)·nH2O)
Hardness: 4-5.5 (Mohs scale), Color: Rusty brown, dark grey, or reddish-brown, Luster: Dull to sub-metallic, Crystal Structure: Amorphous to microcrystalline, Specific Gravity: 3.0-3.9
- Hardness
- 4-5
Identified More sedimentary →
Explore Ironstone concretion in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 4-5.5 (Mohs scale), Color: Rusty brown, dark grey, or reddish-brown, Luster: Dull to sub-metallic, Crystal Structure: Amorphous to microcrystalline, Specific Gravity: 3.0-3.9
Formation & geological history
Formed by the precipitation of mineral cement (iron oxides) within the spaces between sediment grains, often around a nucleus like a leaf or shell. Commonly found in sedimentary basins and riverbeds.
Uses & applications
Historically used as a low-grade iron ore. Today, used primarily as decorative stones, landscaping material, or for geological collecting.
Geological facts
These are often mistaken for meteorites due to their weight and dark appearance. Some concretions, known as 'Moqui Marbles', are found in the Navajo Sandstone of Utah.
Field identification & locations
Identify in the field by their rounded or disc-like shapes, heavy weight for their size, and distinct rusty weathering on the surface. Commonly found in shale or sandstone layers.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary