Definition of: septarium

(sep·târ′ē·əm) noun plural ·tar·i·a (-târ′ē·ə) Geol.
A rock nodule or concretion, usually several feet in diameter and roughly spherical, having a compact crust and an internal mass broken up by angular radiating or intersecting cracks usually filled with a foreign mineral: also called turtlestone. [<NL <L septum an enclosure, wall]
—sep·tar′i·an adjective