Septaria – Boom clay pits, Belgium – 8.1 kg

This septaria comes from the Boom clay pits near Antwerp, Belgium. Formed during the Oligocene, it developed around a clay-rich core that naturally cracked as it dried and contracted. This internal shrinkage created the characteristic polygonal fissures—a kind of geological craquelure.
Later, these fractures were partially filled with calcite, which crystallised in the open spaces. The result is a complex, graphic structure, revealed here by a simple cut through the nodule.
Mounted on a brass base, this specimen quietly demonstrates what time, pressure, and a bit of underground chemistry can achieve—with no embellishment.