Septarian Nodule (Septaria)

Physical Properties

Hardness: 3.5-4 (Mohs); Color: Brown (siderite/clay), Yellow (calcite), Gray (limestone); Luster: Waxy to earthy; Crystal Structure: Trigonal/Orthorhombic; Features unique shrinkage cracks filled with crystals.

Formation & Geological History

Formed during the Cretaceous period (approx. 50-70 million years ago). They began as volcanic eruptions that killed sea life, which then sank and formed mud balls. As the ocean receded, the mud dried and cracked, and decomposing marine life provided minerals that crystallized in the fissures.

Uses & Applications

Primarily used for decorative ornaments, carvings (like the goddess/female torso shape shown), lapidary arts, jewelry, and as educational geological specimens.

Geological Facts

The name 'Septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks/separations in the stone. They are also known as 'Dragon Stones' in some folklore traditions.

Field Identification & Locations

Identify by a 'turtle-back' pattern of cracks or a combination of dark outer mudstone and light yellow crystalline interiors. Most famous deposits are found in Utah, USA and Madagascar.

Identified on: 4/29/2026

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