sedimentary
Septarian Nodule
Septarian Concretion (CaCO3 with Siderite/Limonite streaks)
Hardness: 3.5-4 (Mohs); Color: Tan, brown, white, and yellow; Luster: Dull to waxy; Structure: Microcrystalline with irregular veins; Cleavage: None (conchoidal fracture).
- Hardness
- 3
- Color
- Tan, brown, white, and yellow
- Luster
- Dull to waxy
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Tan, brown, white, and yellow; Luster: Dull to waxy; Structure: Microcrystalline with irregular veins; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) from mud balls and organic matter in ancient seabeds that cracked and were filled with minerals like calcite.
Uses & applications
Primarily used for lapidary work, decorative display pieces, jewelry (cabochons), and collection specimens. Often sliced and polished to show internal 'dragon skin' patterns.
Geological facts
Also known as 'Dragon Stones' due to their scaly appearance. They are unique because they form from the inside out as the core shrinks and cracks.
Field identification & locations
Found in dry lake beds or riverbanks, especially in Utah and Madagascar. Identify by the 'septaria' (cracks) that reveal contrasting mineral fillers against the base rock.
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