Nice, interesting. I am using CYCLES in 2.8 beta.
I am using similar nodes, basically color ramps and voronoi. The problem is, there are many tips of opal (black opals, mexican opals, australian opals, milky opals, fire opals etc… some totally clean and many with dirt and very special inclusions), but many are in part see through, which means surface only effects come out as plastic or give disappointing results.
So from the beginning, I decided that there must be geometry involved, like in real life, many minerals are solidified gases and liquids, so the shapes inside the mineral can’t be obtained with material effects only. It’s even harder if the jewel must be animated.
I am doing this for a specific tutorial, in spanish (i will post nodes then).
Its faster to create variations then, like a bluer opal