sedimentary

Ironstone Concretion

Ironstone (Limonite/Goethite Concretion)

Hardness: 5-5.5; Color: Dark brown to black with reddish-brown earth tones; Luster: Dull to sub-metallic; Structure: Nodular, often displaying concentric layers or a 'mummified' appearance; Specific Gravity: Approx 3.3-4.3

Hardness: 5-5
Color: Dark brown to black with reddish-brown earth tones
Luster: Dull to sub-metallic

Identified July 7, 2026More sedimentary →

Explore Ironstone Concretion 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 the precipitation of mineral cement, typically iron oxides like goethite or limonite, within the spaces between sediment grains. These often grow around a nucleus in sedimentary basins. Period: Various, common in Cretaceous and Jurassic strata.

Uses & applications

Primarily of interest to collectors and geologists; historically used as a low-grade iron ore in local smelting operations.

Geological facts

These are sometimes mistaken for meteorites due to their heavy weight and dark, weathered crust, or for fossils due to their organic-looking bulbous shapes. They are known as 'pseudofossils' when they mimic biological forms.

Field identification & locations

Identify by its high density relative to other stones, streak test (typically yellowish-brown), and characteristic layered or lumpy botryoidal-like outer surface. Common in riverbeds and eroding clay cliffs.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary