it’s a locket with moss agate cabochon cut in drop shape. you can hide something flat or a photo inside. the agate is semi-opaque so the color and pattern on the thing inside changes how the whole pendant looks like. i use it often when i want it to fit the coulor of my dress 
sterling silver and rat tail chain.
click on the photo below to see the possibilities of this locket
2014
the work was exposed on 2015 beijing international metal&jewellery art exhibition BIC-MAJA (beijing world art museum, china).