The nature of a handful of gem grade zinc blende, mostly used for industrial opaque, which is derived from the China Inner Mongolia yellow green zinc blende, accidental opportunity only got this piece of stone, you can see it in the prototype by below. The 2.369 is the index of refraction of sphalerite, the scattered light is very strong, this feature was destined it is natural gemstone. 

We in the gem chooses the material carefully

Gem grinding studio we

We collect gem material in the mine, the first hand source.