sedimentary
Septarian Nodule (Sphere)
Septarian (composed of Calcite, Aragonite, and Limestone/Claystone)
Hardness 3.5-4 (Mohs); color: yellow-tan (calcite centers), brown (aragonite lines), and grey (limestone exterior); waxy to vitreous luster; often polished into spheres.
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Physical properties
Hardness 3.5-4 (Mohs); color: yellow-tan (calcite centers), brown (aragonite lines), and grey (limestone exterior); waxy to vitreous luster; often polished into spheres.
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago). They began as mud balls that cracked as they dried; minerals like calcite and aragonite then crystallized inside the cracks.
Uses & applications
Primarily used for decorative purposes, ornamental carvings, jewelry, and as a popular collector's specimen.
Geological facts
Also known as 'Dragon Stone.' The name 'septarian' comes from the Latin word 'septum,' meaning a partition, referring to the cracks that divide the internal sections.
Field identification & locations
Commonly found in Utah (USA) and Madagascar. To identify, look for the distinct cracked pattern filled with yellow minerals against a grey or brown matrix.
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