sedimentary
Septarian Nodule
Septarian concretion (Complex mixture of Siderite, Calcite, and Aragonite)
Hardness: 3.5-4 (Mohs); Color: Brown, tan, and cream; Luster: Dull/earthy exterior, vitreous interior; Structure: Microcrystalline with distinct shrinkage cracks (septaria); Specific Gravity: 2.7-3.4
- Hardness
- 3
- Color
- Brown, tan, and cream
- Luster
- Dull/earthy exterior, vitreous interior
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Brown, tan, and cream; Luster: Dull/earthy exterior, vitreous interior; Structure: Microcrystalline with distinct shrinkage cracks (septaria); Specific Gravity: 2.7-3.4
Formation & geological history
Formed during the Cretaceous period (approx. 50-70 million years ago) in marine environments. They originate as mud balls that dry out, crack, and are later filled with mineral deposits like calcite.
Uses & applications
Primarily used as decorative display specimens, paperweights, in lapidary work for cabochons, and occasionally in metaphysical collections.
Geological facts
The word 'septarian' comes from the Latin 'septum' meaning partition, referring to the cracks that divide the nodule. They are often called 'Dragon Stones' due to their scaly appearance.
Field identification & locations
Identify in the field by looking for rounded, heavy nodules with a net-like pattern of cracks on the surface. Commonly found in Utah, USA, and Madagascar. When cracked open, they often reveal beautiful yellow calcite crystals.
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