sedimentary
Septarian Nodule
Septarian Concretion (Composition: Calcite, Aragonite, and Limestone/Clay)
Hardness: 3.5 to 4 on Mohs scale; Color: Brown, grey, and yellow with dark centers; Luster: Vitreous to earthy; Crystal structure: Trigonal/Orthorhombic (inner minerals); Cleavage: Perfect rhombohedral in calcite portions; Specific gravity: 2.7.
- Hardness
- 3
- Color
- Brown, grey, and yellow with dark centers
- Luster
- Vitreous to earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3.5 to 4 on Mohs scale; Color: Brown, grey, and yellow with dark centers; Luster: Vitreous to earthy; Crystal structure: Trigonal/Orthorhombic (inner minerals); Cleavage: Perfect rhombohedral in calcite portions; Specific gravity: 2.7.
Formation & geological history
Formed during the Cretaceous period (approx. 50-70 million years ago) from the accumulation of sedimentary matter around a core. As the mud balls dried and shrank, they cracked, and calcite/aragonite precipitated into the fractures from groundwater.
Uses & applications
Primarily used as ornamental display pieces, home decor, and lapidary crafts (cabochons and bookends). It is also highly valued by mineral collectors for its unique 'dragon skin' appearance.
Geological facts
Also known as 'Dragon Stone' due to its scale-like patterns. These nodules are unique because they represent a combination of biological and chemical processes, often containing fossilized remains at their center.
Field identification & locations
Identify in the field by looking for spherical or potato-shaped mudstone rocks with visible star-shaped cracks. Common locations include Utah (USA), Madagascar, and various parts of the UK. Collectors should look for high contrast between the yellow calcite and dark limestone.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary