Septarian SphereThis sphere is carved from septarian, a unique rock formed from a combination of minerals including calcite, aragonite, and limestone. Septarian nodules develop when mineral rich mud cracks and fills with calcite or aragonite over millions of years, creating striking patterns of yellow, brown, and gray. Why you'll love this: Material: Septarian (limestone with calcite and aragonite) Size: Approximately 2 to 2. 5 inches in diameter Appearance: Polished