sedimentary
Septarian (Dragon Stone)
Septarian concretion (Calcite, Aragonite, and Limestone)
Hardness: 3.5-4 (Mohs); Color: Yellow (Calcite), Brown (Aragonite), Gray (Limestone); Luster: Vitreous to dull; Structure: Concretionary with trigonal crystals; Cleavage: Perfect rhombohedral in calcite portions.
- Hardness
- 3
- Color
- Yellow (Calcite), Brown (Aragonite), Gray (Limestone)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Yellow (Calcite), Brown (Aragonite), Gray (Limestone); Luster: Vitreous to dull; Structure: Concretionary with trigonal crystals; Cleavage: Perfect rhombohedral in calcite portions.
Formation & geological history
Formed roughly 50 to 70 million years ago during Earth's Cretaceous period. They began as mud balls on the seafloor that cracked as they dried, with minerals later precipitating into those cracks.
Uses & applications
Primarily used for ornamental purposes, home decor, lapidary arts, and as a popular specimen for mineral collectors. Frequently carved into spheres, eggs, or towers.
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, ancient appearance.
Field identification & locations
Identify by the distinct pattern of yellow calcite centers surrounded by brown aragonite dividers within a gray limestone matrix. Commonly found in Utah, USA and Madagascar. Best identified by the three-tone angular patterns.
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