sedimentary
Septarian Nodule (Septarian Stone)
Septarian Concretion (CaCO3 with Siderite/Calcite/Aragonite)
Hardness: 3.5-4 (Mohs); Color: Tan, brown, and yellow; Luster: Waxy to dull; Structure: Microcrystalline with distinct crack patterns (septaria) filled with calcite; Specific Gravity: 2.6-2.7
- Hardness
- 3
- Color
- Tan, brown, and yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Tan, brown, and yellow; Luster: Waxy to dull; Structure: Microcrystalline with distinct crack patterns (septaria) filled with calcite; Specific Gravity: 2.6-2.7
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago). They began as sedimentary clay balls that dried and cracked, with mineral-rich water later depositing calcite or aragonite into the shrinkage cracks.
Uses & applications
Primarily used for jewelry (cabochons), ornamental decor, lapidary art, and geological specimen collecting.
Geological facts
Also known as 'Dragon Stone' because the crack patterns look like dragon scales. Most high-quality specimens come from Southern Utah or Madagascar.
Field identification & locations
Identify by looking for distinct yellow/brown 'lightning bolt' veins or angular patterns against a grey or tan mudstone backdrop. Often found in dry lake beds or shale deposits.
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