Dragonstone – Carnegie Museum, Forbes Avenue, Pittsburgh, Pennsylvania

This beautiful Septarian nodule, on display at the Carnegie Natural Histpry Museum in Pittsburgh, is from England. Septarian Nodules, also called Dragonstone, are concretions of sedimentary rock containing radiating fissures called "septaria", (from the Latin word septum; meaning "partition", referring to the cracks/separations in this stone). Septarian cavities fill with clay ironstone and the radiating fissures usually contain crystals of buttery calcite, though siderite or pyrite coatings are also occasionally present showing bright reddish and golden colours. In many cases, the brown tones are aragonite, the grey parts are limestone and the white or clear sections are barite. Some septaria may also contain small calcite stalagtites and well-shaped millimetric pyrite single crystals.