sedimentary
Ironstone Concretion / Goethite-Hematite Geode
Goethite / Hematite Concretion (Fe3O4 / FeO(OH) / Fe2O3)
Hardness: 5.0-5.5 on Mohs scale. Color: Dark brown, reddish-orange rust interior with metallic greyish-black goethite/hematite veins and crusts. Luster: Earthy to metallic. Crystal structure: Amorphous to microcrystalline, often forming botryoidal or hollow septarian-like structures.…
- Hardness
- 5
- Luster
- Earthy to metallic
Identified More sedimentary →
Explore Ironstone Concretion / Goethite-Hematite Geode in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5.0-5.5 on Mohs scale. Color: Dark brown, reddish-orange rust interior with metallic greyish-black goethite/hematite veins and crusts. Luster: Earthy to metallic. Crystal structure: Amorphous to microcrystalline, often forming botryoidal or hollow septarian-like structures. Cleavage: None, irregular to subconchoidal fracture. Specific Gravity: 3.3-4.3 (noticeably heavy).
Formation & geological history
Formed by chemical precipitation of iron compounds around a nucleus (often organic or mineral matter) within sedimentary rock host layers such as sandstone or shale. Weathering dissolves surrounding materials, leaving behind hollowed, vuggy ironstone concretions.
Uses & applications
Primarily collected as geological curiosity specimens or lapidary display pieces. Historically mined locally as low-grade iron ore.
Geological facts
These ironstone nodules are often called 'rattlesnakes' or 'indian paint pots' when filled with soft loose clay or powder inside. When broken open, the contrast between the dark metallic goethite shell and the bright reddish iron oxides creates intricate cave-like formations.
Field identification & locations
Field identification involves checking high specific gravity (heavy feel), magnetic response (weak to moderate), earthy reddish-brown exterior shell, and hollow interior coated in dark botryoidal or fibrous iron oxides. Very common in sedimentary basins worldwide.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale
Argillaceous sedimentary rock
sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary