This is a concretion of rock, formed from a calcium-rich clay that hardened into a limestone nodule. Later, the rock shrank, creating cracks that were then filled with water in which calcite crystal formed. The angular cracks are called septaria which comes from the Greek word ‘septum’ meaning partition.

Septarian nodule

Common Name

Septarian nodule

Scientific Name

Type

Rocks and Pseudofossils

Strata

Oxford Clay

Time Period

Upper Jurassic

Age

160 million years

Where Found

Furzy Cliff

Found By

Unknown

Museum

Dorset

Accession Number

DCM.G.04151