Test rendering of a round brilliants modeled using my gem cut Houdini tool:
https://www.artstation.com/artwork/r9GEoE
It's been a long time since I first rendered the brilliant model: https://vimeo.com/30343806
Then there was no dispersion in the standard shader. So, I have to develop my own dispersion mantra shader.
Now there is the Dispersion parameter in the Principled Shader.