sedimentary

Ironstone Concretion / Goethite-Hematite Geode

Goethite / Hematite Concretion (Fe3O4 / FeO(OH) / Fe2O3)

AI-generated identification · may be incorrect

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 July 24, 2026More sedimentary →

Explore Ironstone Concretion / Goethite-Hematite Geode in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

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.