This Natural Brown Zircon with brilliant flashes of Yellow & Orangish rays that radiate throughout the stone is from the country of Cambodia. A gemstone with a high refractive Index and wonderful array of dispersion in color.
It's a little less visible to the unaided eye, but as we view the stone under magnification, you can notice the top facet junctions (crown facets) of the stone appear to be sharp. As we slightly tilt and look down through the table into the stone's belly (pavillion), we begin to see what appears to be an optical distortion.
In doubly refractive stones, the light splits in two, traveling and bending at different speeds This fuzziness and doubling effect is an indication of strong, double refraction as well as high birefringence.
Double or single refraction is dependent on the gemstone or minerals Crystal system. Zircon falls into the tetragonal crystal system. Although all doubly refractive stones will have a measurement of birefringence, its the high variable in Zircon that makes this optical property so visible.
The speed at which light passes through, refracts and bends in a gemstone is a measurement of its Refractive Index.
Zircon 1.925 to 1.984 (+/- 0.040)
The Birefringence is a variable measurement between the lowest and highest indice.
0.000 to 0.059
As the stone is viewed at a little more distance you can see the dispersion of the colors & the light playing beautifully together! That is what we call '"Fire" in a stone !