sedimentary

Ironstone Concretion

Siderite or Hematite Concretion

AI-generated identification · may be incorrect

Hardness: 5-6 (Mohs); Color: Tan/yellow outer shell with a dark reddish-brown iron-rich core; Luster: Dull/Earthy; Structure: Nodular/Amorphous; Cleavage: None; Specific Gravity: 3.0-3.9

Hardness: 5-6 (Mohs)
Luster: Dull/Earthy

Identified April 11, 2026More sedimentary →

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Physical properties

Hardness: 5-6 (Mohs); Color: Tan/yellow outer shell with a dark reddish-brown iron-rich core; Luster: Dull/Earthy; Structure: Nodular/Amorphous; Cleavage: None; Specific Gravity: 3.0-3.9

Formation & geological history

Formed through the precipitation of mineral cement (typically iron oxides or carbonates) in the spaces between sediment grains, often around a nucleus such as a leaf, bone, or shell. These typically form in sedimentary basins over millions of years.

Uses & applications

Primarily used as geological curiosities for collectors; historically some high-iron concretions were used as iron ore. Some are used in landscaping or decorative masonry.

Geological facts

Many people mistake the interior patterns of broken concretions for fossils or organic remains like hearts or organs due to their distinct color zoning. This example shows an iron-rich 'nucleus' interior inside a sandy outer rind.

Field identification & locations

Identify by looking for rounded, pebble-like stones that appear heavier than they look and show concentric bands of different colors when broken. Common in riverbeds and eroded sandstone cliffs.