selenite

n. [ Gr. &unr_; dart, fr. &unr_; dart, fr. &unr_; to throw: cf. F. bélemnite. ] (Paleon.) A conical calcareous fossil, tapering to a point at the lower extremity, with a conical cavity at the other end, where it is ordinarily broken; but when perfect it contains a small chambered cone, called the phragmocone, prolonged, on one side, into a delicate concave blade; the thunderstone. It is the internal shell of a cephalopod related to the sepia, and belonging to an extinct family. The belemnites are found in rocks of the Jurassic and Cretaceous ages. -- Bel*em*nit"ic, a. [1913 Webster]