Fire of a Diamond

You often hear that only a diamond exhibits the optical quality called fire. Fire means more than just flashing in the light; it means flashing with many colors. The effect comes from refraction, the same phenomenon that makes a glass prism turn sunlight into a rainbow. Diamond is so much more refractive than glass that even the small stones most of us are acquainted with can do the job. But one other gemstone is capable of showing fire, zircon. It takes careful observation in a sunbeam, but I can confirm that it's true—a tiny cut diamond shows it clearly, and a one-carat cut zircon I have shows a definite glimmer of fire. But a faceted quartz stone in my possession, while it glitters well enough, is dead to fire. Supposedly benitoite shows fire, too, but good crystalline specimens, let alone decent cut stones, are rarer than hen's teeth.
_{Photo from Lars Plougmann on flickr.com under Creative Commons license}