Septarian Nodule (Dragon Stone)
Septarian concretion (Calcite following Siderite/Aragonite in Claystone) · Semi-Precious Gemstone / Collector Mineral Specimen
Crystal System
Trigonal (Calcite center) and Orthorhombic (Aragonite walls); typically occurs in a massive, nodular, or geode-like habit with radiating cracks.
Mineral Group
Carbonate (sub-group: Calcite/Aragonite), within a Sedimentary Clay matrix.
Chemical Formula
CaCO3 (Calcite/Aragonite) + Al2Si2O5(OH)4 (Bentonite Clay) + Hydrated Iron Oxides (Limonite)
Formation Process
Sedimentary. Formed via chemical precipitation around an organic nucleus in seafloor mud (Bentonite clay). Shrinkage cracks (septaria) formed as the mud dried and were later filled with Calcite or Aragonite crystals via mineral-rich groundwater infiltration.
About This Crystal
The specimen shows dark, earthy clay matrix surrounding a vug or vein lined with druzy crystals. The center features brownish-black to amber-colored druzy crystals with a vitreous to sub-metallic luster. Ranging from opaque matrix to translucent crystals, it displays characteristic internal shrinkage cracks or 'septa.'
Physical Characteristics
Color: Dark grey/brown matrix with yellow/brown crystals. Streak: White to pale brown. Cleavage: Perfect rhombohedral in Calcite areas. Fracture: Conchoidal to uneven. Specific Gravity: 2.60 - 2.80. Fluorescence: Some specimens show yellow or white fluorescence under UV light.
Optical Properties
Refractive Index: 1.486 - 1.658 (varies by component). Birefringence: Strong (0.172). Doubly refractive. Displaying a vitreous luster on crystal faces and a dull, earthy luster on the matrix.
Hardness & Durability
Origin Region
Notable sources include Utah (USA), Madagascar, and Morocco. Formed in ancient sea beds where volcanic debris and decomposing sea life created mineral-rich mud.
Hardness & Durability
Mohs Hardness: 3.5 to 4.0. It is a relatively soft and brittle material. Low toughness makes it prone to scratching or cracking if dropped. Not recommended for high-wear jewelry.
Care & Maintenance
Clean with a soft, damp cloth and mild soap only. Avoid ultrasonic cleaners, steam, and harsh chemicals (acids will dissolve carbonate components). Store separately from harder stones like quartz or diamonds to prevent scratching.
Rarity & Value
Relatively common. Value depends on the aesthetics of the 'pattern,' crystal size within the cracks, and overall size. Polished spheres and large nodules command higher prices. Treatments are rare, though some are stabilized with resins.
Special Characteristics
The distinctive 'cracked' appearance formed by desiccation (shrinking) is unique. Some samples feature 'enhydro' cavities or druzy crystal linings within the septa, creating a geode-like interior.
Lore & History
Historically used as a 'Dragon Stone' in folklore due to its resemblance to dragon scales. In metaphysical traditions, it is believed to be a grounding stone that enhances communication and patience (not a scientific claim).