Septarian Nodule

Physical Properties

Hardness: 3.5-4 (Mohs); Color: Brown, yellow, cream, and grey; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Indistinct; Specific Gravity: 2.7-2.9.

Formation & Geological History

Formed during the Cretaceous period (50-70 million years ago) within muddy sea floors. As sea levels receded, mud balls dried and cracked, subsequently filling with calcite, aragonite, and limestone.

Uses & Applications

Mainly used for ornamental purposes, including polished cabochons for jewelry, home decor carvings, and lapidary collection specimens.

Geological Facts

The name comes from the Latin word 'septum' meaning partition, referring to the cracks that divide the concretion. They are also nicknamed 'Dragon Stones' due to their scaly, cracked appearance.

Field Identification & Locations

Identify by the characteristic 'cracked' appearance with yellow or white calcite filling the dark brown matrix. Often found in dry lake beds and areas with bentonite clay, notably in Utah and Madagascar.

Identified on: 5/3/2026

Mode: Standard