Since it's all in Blender, and not meant for game export, you could use internal geometry for those parts. Then use a material on the surface that refracts the insides. I edited your thread title to include [Blender] since it helps to indicate your questions are specific to Blender, and will get you more eyeballs from…
Here's and example: https://blenderartists.org/forum/attachment.php?attachmentid=407424&d=1446128240 I wanna understand how I would go about adding the bubbles, I think the texture would be easy, just create a bump and spec map, but what about the insides of the crystal? Here's another good…