The material itself is entirely up to your personal preference.
The real trickery lies in roughness, reflections, light refraction and shininess. Crystals would become more “alive” with effects such as those, but with very fine tweaking. Again the end result is your personal preference.
Here’s an unreal doc I suggest you read through and get a feel for. once you get through it I have a good feeling you’ll feel much more comfortable with creating what you’re looking for! 