Abstract: We present an algorithm for rendering faceted colored gemstones in real time, using graphics hardware. Beyond the technical challenge of handling the complex behavior of light in such objects, a real time high quality rendering of gemstones has direct applications in the field of jewelry prototyping, which has now become a standard practice for replacing tedious (and less interactive) wax carving methods. Our solution is based on a number of controlled approximations of the physical phenomena involved when light enters a stone, which permit an implementation based on the most recent -- yet commonly available -- hardware features such as fragment programs, cube-mapping and floating-point rendering.