sedimentary
Septarian Nodule (Dragon Stone)
Septarian Nodule (Calcium Carbonate/Aragonite/Calcite Concretion)
Hardness: 3.5 to 4 (Mohs); Color: Brown, yellow, grey, and tan; Luster: Dull to waxy; Crystal structure: Trigonal/Orthorhombic; Cleavage: Perfect rhombohedral (calcite portions); Specific gravity: 2.6 - 2.8
- Hardness
- 3
- Color
- Brown, yellow, grey, and tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 3.5 to 4 (Mohs); Color: Brown, yellow, grey, and tan; Luster: Dull to waxy; Crystal structure: Trigonal/Orthorhombic; Cleavage: Perfect rhombohedral (calcite portions); Specific gravity: 2.6 - 2.8
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) when volcanic eruptions killed sea life that sank to the ocean floor. Sediments accumulated around the organic matter, forming a nodule. As the ocean receded, the nodules dried and cracked, and calcite/aragonite crystallized within the shrinkage cracks.
Uses & applications
Primarily used for decorative purposes, lapidary arts (cabochons and spheres), spiritual/metaphysical collecting, and as a educational geological specimen.
Geological facts
Also known as 'Dragon Stones' due to their scaly, reptilian appearance. They are unique because they are a combination of different minerals: yellow calcite, brown aragonite, and grey limestone/bentonite.
Field identification & locations
Identify in the field by looking for 'turtle-back' patterns on a rounded exterior or by the presence of yellowish-white crystalline veins inside a mudstone exterior. Commonly found in Utah, USA and Madagascar. Best found in dry lake beds or river banks where erosion has exposed Cretaceous layers.
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