Hmm let me see if I can help here.
If you’re using substrate, you’ll likely have a lot of luck getting a realistic diamond look due to its layering system and real-world values. That being said, Substrate is a relatively untouched feature so it’s very difficult to learn and find assets for. Here’s probably the closest you’ll get:
Now, for traditional materials, this effect would need to be completely faked, as materials contain no actual depth values for realistic light dispersion. This is a very advanced effect so it is unlikely you will be able to find a good version of it for sale.
What basic pieces would that entail?
-A modeled raised surface
-An interior texture with a bump map offset to fake depth. The texture and height map would have to be carefully crafted
-A version of the texture with colors, which with some math can randomly show colors / brightness based on camera angle (similar to this tutorial https://www.youtube.com/watch?v=pSRM3n14k3A)
Here are some assets / tutorials that should give you a good jumping off point:
TLDR: It can be done, but if you’re not a technical artist you’re likely in way over your head.