sedimentary
Septarian Nodule Geode
Septarian concretions (composed of Calcite, Aragonite, and Limestone)
Hardness: 3-4 (Calcite/Aragonite) / color: brown, yellow, and grey / luster: vitreous to dull / crystal structure: rhombohedral / cleavage: perfect rhombohedral / specific gravity: 2.71
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3-4 (Calcite/Aragonite) / color: brown, yellow, and grey / luster: vitreous to dull / crystal structure: rhombohedral / cleavage: perfect rhombohedral / specific gravity: 2.71
Formation & geological history
Formed in ancient sea beds roughly 50 to 70 million years ago during the Cretaceous period. Decomposing sea life killed by volcanic eruptions caused mud balls to form, which then cracked and were filled with mineral deposits like calcite.
Uses & applications
Primarily used as decorative display pieces, in lapidary work for making bookends and spheres, and as a popular specimen for mineral collectors.
Geological facts
The name comes from the Latin word 'septum' meaning wall or partition, referring to the cracks and separations between the different minerals. They are often called 'Dragon Stones' due to their scaly appearance.
Field identification & locations
Identify by the unique angular patterns of yellow/brown calcite filling cracks within a mudstone/limestone matrix. Commonly found in Utah, USA and Madagascar.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary