Polymer clay is a great material for making imitative pieces – replica foods and faux stones some of my favourites. Mokume Gane, a flexible polymer clay technique, is great for making beautiful abstract designs. Turns out, with careful picking and layout, it also makes great faux stones. Using good picks, you can imitate the vein and cell structure of jaspers and other stones by doing a classic mokume gane stack.
The tutorial offers a wealth of pictures and links.