sedimentary

Iron Concretion

Iron oxide concretion (Hematite or Goethite)

AI-generated identification · may be incorrect

Hardness varies (5-6 for hematite, 5-5.5 for goethite), color is dark brown to black, submetallic to earthy luster, often botryoidal or nodular structure, no cleavage, high specific gravity.

Identified August 31, 2026More sedimentary →

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Physical properties

Hardness varies (5-6 for hematite, 5-5.5 for goethite), color is dark brown to black, submetallic to earthy luster, often botryoidal or nodular structure, no cleavage, high specific gravity.

Formation & geological history

Formed in sedimentary rocks by the precipitation of iron oxide minerals from aqueous solutions, often around a nucleus. They can form over various geological ages.

Uses & applications

Often collected as curiosities, sometimes mistaken for meteorites (meteor-wrongs). Historically, large deposits have been used as iron ore.

Geological facts

They frequently exhibit unusual shapes, leading people to mistake them for fossils or meteorites. Moqui Marbles are a famous type of iron concretion.

Field identification & locations

Identify by their relatively high density, dark color, and characteristic nodular shapes. A streak test will usually leave a reddish-brown (hematite) or yellowish-brown (goethite) streak. Commonly found in sandstone or shale formations.