Yet nother take on minerals.
Years ago I’ve been positively struck by the works of @ivaydesign, who produced some fascinating crystals with some esoteric-looking materials: they looked like having internal irregularities and impurities under the surface, but apparently no volumetrics or added geometry were used.
I really wanted to sort of reproduce his approach.
I think I’ve got it close.
However I ask myself whether this approach is practical: the eventual image took 3h 47m to get rendered with GPU (NVidia Geforce GTX 1050Ti). The shortest time, actually. At one point Blender ‘promised’ me 33 hours of rendering, and I have reworked the material (cursing badly, you know).
The main crystal is basically a mix of just three Principled BSDFs (smaller whitish crystals comprise the earlier discarded versions of the main crystals material, and a simple glass combo has been added for the smallest).
I did some very simple fake fresnel effect, but more important was the Edge Detect nodegroup by Wayward Art Company (this one - https://www.blendernation.com/2018/10/22/edge-detect-node-for-blender-2-8/).
It has its problems, though: when any type of bevelling is employed, the space between new edges becomes darker and it looks nasty. I tried to use some tricks to tone it down (or, rather lighten it up), but with a very low level of success, so I ended up removing geometric bevel completely.
Finetuning the materials took slightly less than 3 weeks. The eventual nodetree (last image; orange parts comprise several nodegroups with quite a lot of extra noodlework inside) ended up so snarly that I was afraid it would start barking, or phasing in and out of time, or that it would become self-aware, gain self-esteem and start verbally abusing me for being that slow and dim-witted, etc. 
I have become quite obsessed with this project - literally - at the expense of night sleep and daily routines sometimes.
But I think it was worthwhile. Well, maybe.
Render time: 3h 47m (Cycles).
PC: Dell Inspiron 15 7000, CPU: Core i7-7700, 2.80GHz, GPU: NVidia Geforce GTX 1050Ti.