This is a large, grass green & brown Plum Blossom Jasper pendant/necklace. It's done in the shape of a teardrop, and is an excellent example of this form of Jasper. It comes with a nice black-coated pewter bail, as well as the 18" necklace.
Jasper is a form of chalcedony quartz, and is opaque rather than clear or translucent like regular quartz or agate. It contains an abundance of impurities which give its interesting appearance.