Septarian Nodule (also known as Dragon Stone)
Septarian Calcite/Aragonite Concretion · Mineral Specimen / Decorative Stone
Crystal System
Trigonal (Calcite) and Orthorhombic (Aragonite); typically occurs in a massive, microcrystalline, or concretionary habit.
Mineral Group
Carbonates (specifically a mixture of Calcite and Aragonite within a clay-rich sedimentary rock)
Chemical Formula
CaCO3 (Calcite/Aragonite) with SiO2 (Chalcedony/Quartz) and Clay Minerals
Formation Process
Sedimentary. Formed during the Cretaceous period when minerals crystallized in cracks (septaria) formed by the shrinking of dehydrating clay nodules on the seafloor.
About This Crystal
A polished, rounded nodule featuring a contrast between a tan/grey clay-rich limestone exterior and dark brown or yellow crystalline interiors. It displays a waxy to vitreous luster and is generally opaque to translucent in the crystalline sections.
Physical Characteristics
Color: Grey, tan, and dark brown. Streak: White. Cleavage: Perfect rhombohedral (in crystalline parts). Fracture: Conchoidal to uneven. Specific Gravity: 2.6 – 2.8. Fluorescence: Often shows yellow or white under UV light.
Optical Properties
Refractive Index: 1.48 - 1.66. Birefringence: Strong (in calcite sections). Generally lacks pleochroism due to the microcrystalline structure of the matrix.
Hardness & Durability
Origin Region
Commonly found in Utah (USA), Madagascar, and Morocco; typically forms in marine sedimentary seafloors.
Hardness & Durability
Mohs Hardness: 3.5 to 4. Low durability; very sensitive to scratching and impact. Not recommended for high-wear jewelry.
Care & Maintenance
Avoid ultrasonic cleaners and steam. Clean only with warm, soapy water. Keep away from acids (will dissolve) and harsh chemicals. Store separately to prevent scratches.
Rarity & Value
Common. Value is determined by the complexity of the internal patterns and size. Prices are generally affordable ($5 - $100+ for large specimens).
Special Characteristics
The distinctive 'lightning bolt' or 'dragon scale' patterns (septaria) are unique to this formation. Some specimens contain hidden druzy quartz or calcite crystals in internal vugs.
Lore & History
Historically used as a 'protective' stone; in traditional lore, it is believed to enhance grounding and communication. Known as Dragon Stone due to its resemblance to dragon scales in ancient folklore.