The basic recipe for a faux jade / aventurine in polymer clay is translucent mixed with a small amount of green (or several greens). Add a little bit of dried herbs, mica powders, paints, or what not if you want inclusions or matrix patterns. Form your pieces without mixing up the colours too much. Cure, sand, sand some more, and buff like a mad woman. Joe Patouille’s YouTube tutorial is a nice step through of it.