sedimentary
Septarian Nodule
Septarian Concretion (CaCO3 + CaMg(CO3)2)
Hardness: 3.5-4 (Mohs); Color: Brown, yellow, cream, and grey; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Indistinct; Specific Gravity: 2.7-2.9.
- Hardness
- 3
- Color
- Brown, yellow, cream, and grey
- Luster
- Waxy to dull
Identified More sedimentary →
Explore Septarian Nodule in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3.5-4 (Mohs); Color: Brown, yellow, cream, and grey; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Indistinct; Specific Gravity: 2.7-2.9.
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) within muddy sea floors. As sea levels receded, mud balls dried and cracked, subsequently filling with calcite, aragonite, and limestone.
Uses & applications
Mainly used for ornamental purposes, including polished cabochons for jewelry, home decor carvings, and lapidary collection specimens.
Geological facts
The name comes from the Latin word 'septum' meaning partition, referring to the cracks that divide the concretion. They are also nicknamed 'Dragon Stones' due to their scaly, cracked appearance.
Field identification & locations
Identify by the characteristic 'cracked' appearance with yellow or white calcite filling the dark brown matrix. Often found in dry lake beds and areas with bentonite clay, notably in Utah and Madagascar.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary