Zircon

Zircon is the oldest mineral on earth and, confusingly, has nothing to do with cubic zirconia. It is a genuine natural gemstone with a refractive index high enough to produce real fire.

Sri Lanka produces zircon in green, blue, golden and colourless, and the stones are almost always untreated. The colourless material is the closest natural stone to diamond in dispersion — it genuinely sparkles.