sedimentary
Septarian Nodule
Septarian concretion (Calcite, Aragonite, and Limestone)
Hardness: 3.5 - 4 (Mohs scale); Color: Brown/Grey limestone with yellow calcite veins; Luster: Waxy to dull; Crystal structure: Trigonal (calcite); Specific gravity: 2.7
- Hardness
- 3
- Color
- Brown/Grey limestone with yellow calcite veins
- Luster
- Waxy to dull
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Physical properties
Hardness: 3.5 - 4 (Mohs scale); Color: Brown/Grey limestone with yellow calcite veins; Luster: Waxy to dull; Crystal structure: Trigonal (calcite); Specific gravity: 2.7
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) through the dehydration of clay-rich mud balls on the ocean floor, which cracked and were later filled by mineral deposits like calcite.
Uses & applications
Primarily used as decorative display specimens, lapidary carvings, bookends, and in jewelry as cabochons or tumbled stones.
Geological facts
The name comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the concretion. They are often called 'Dragon Stones' due to their scaly appearance.
Field identification & locations
Identified by the distinct 'lightning' pattern of yellow/white veins against a darker host rock. Often found in dry lake beds or along shorelines in locations like Utah and Madagascar.
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