This stone is called a doublet: a compilation of two natural stones into one. The top layer is a transluscent plume agate, and the bottom layer is black jasper. The thin epoxy that joins the two is sky blue.
 
Heart-shaped plume agate doublet set in a fine silver bezel with etched sterling backplate in a lightburst pattern. Sterling ornamentation and twisted hoop bail. Hung on a 24" glittering diamond-cut beaded sterling chain.
 
Pendants approx. 1.4".