sedimentary
Septarian Nodule (Dragon Stone)
Septarian concretion (composition: Calcium Carbonate / Calcite, Aragonite, and Limestone/Clay)
Hardness: 3.5-4.0 (Mohs scale); Color: Yellow (Calcite), Brown (Aragonite), Gray (Limestone); Luster: Vitreous to dull; Crystal structure: Trigonal (Calcite) / Orthorhombic (Aragonite); Cleavage: Perfect rhombohedral in calcite portions.
- Hardness
- 3
- Color
- Yellow (Calcite), Brown (Aragonite), Gray (Limestone)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 3.5-4.0 (Mohs scale); Color: Yellow (Calcite), Brown (Aragonite), Gray (Limestone); Luster: Vitreous to dull; Crystal structure: Trigonal (Calcite) / Orthorhombic (Aragonite); Cleavage: Perfect rhombohedral in calcite portions.
Formation & geological history
Formed during the Cretaceous period (approx. 50-70 million years ago). They originated as mud balls on the seafloor that cracked due to dehydration and shrinkage; the cracks were subsequently filled by mineral-rich waters precipitating calcite and aragonite.
Uses & applications
Primarily used as decorative display specimens, lapidary carvings (hearts, spheres), jewelry (cabochons), and for metaphysical healing practices.
Geological facts
Also known as 'Dragon Stones' due to their scaly, reptilian appearance. They are essentially fossilized mud bubbles. The name comes from the Latin 'septum' (partition) or 'saeptum' (enclosure), referring to the cracks that divide the nodule.
Field identification & locations
Identified in the field as dull, round mud-colored concretions that reveal 'turtle-back' patterns when cracked open. Significant deposits are found in Utah (USA) and Madagascar. To identify, look for the unique angular 'septaria' patterns separating different mineral colors.
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