sedimentary

Ironstone Concretion

Siderite or Hematite Concretion

AI-generated identification · may be incorrect

Hardness: 5-6 (variable), Color: Rusty brown, ochre, to dark gray, Luster: Dull/Earthy, Crystal Structure: Amorphous or fine-grained crystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 3.0-3.8

Identified June 10, 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 in the spaces between particles of sediment. Often forms in marine or lakeside sedimentary rocks when minerals crystallize around a nucleus like a shell or leaf fragment.

Uses & applications

Used historically as a source of iron ore. Today, they are primarily of interest to collectors or used in decorative landscaping.

Geological facts

Concretions are often mistaken for fossils, eggs, or meteorites due to their unusual shapes. Some, known as 'Septarian nodules,' have hollow interiors with beautiful crystal linings.

Field identification & locations

Identify in the field by their rounded or ovate shapes and rusty, weathered exterior. They are commonly found in eroding shale or sandstone cliffs. Collectors look for them to crack open in hopes of finding fossils or crystals inside.