Can someone enlighten me on modeling and rendering gemstones? Like: http://i01.i.aliimg.com/photo/v1/123125317/Labradorite_Natural_Calibrated_Cabochons_Faceted_Gemstones_Wholesale.jpg or http://image.made-in-china.com/2f0j00LeSTDQOthCgA/Fashion-Jewelry-Loose-Faceted-Gemstone-SEMI001-.jpg etc etc.