I am trying to create a game with lots of crystals, sadly there no much tutorials on creating crystals(only the basic glass crystals, that are just glass material on crystal mesh). If anyone have some tutorials or tips I be really grateful 
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 āaliveā with effects such as those, but with very fine tweaking. Again the end result is your personal preference.
Hereās an unreal doc I suggest you read through and get a feel for. once you get through it I have a good feeling youāll feel much more comfortable with creating what youāre looking for! 
Thanks I will read it hopefully I will get better results