Begin by taking a look at the material in which you want to replicate. In this case, I looked through some crystals, looking for the closest match to your reference image.

I came across Phenakite, https://www.crystalage.com/online_sto.../phenakite.cfm

I then looked up it's IOR, which is 1.65

Then, you need to make some maps. Take a look at this tutorial here: https://web.archive.org/web/200903270...m/TUTO-ice.htm