Making Iridescent Rocks

[ares2101]

I'm working on a scene for one of those Carbon Planets, made of carbides rather than silicates.  While researching the materials, I noticed how Silicon Carbide can form these really cool iridescent crystal patterns.  Is there a way to make this effect?  I figure a reflective shader broken up with a fractal can produce the variable reflectivity you get in rocks, but I have no idea how to create this variable color effect.
Seriously, that's just gorgeous.  I want to make glittery black cliffs of this stuff.

[Dune]

You can give reflection different colors, but can't use any function I'm afraid. The only possibility I see is the reflectivity image or function input in a default shader. Try a colorful PF, and a small roughness and index of 7 or so, metalness on, see what that does. You probably need fake stones in several sizes to make up teh crystal hard shapes.

[ares2101]

You can give reflection different colors, but can't use any function I'm afraid. The only possibility I see is the reflectivity image or function input in a default shader. Try a colorful PF, and a small roughness and index of 7 or so, metalness on, see what that does. You probably need fake stones in several sizes to make up teh crystal hard shapes.

Didn't try the hard crystal shapes yet as time is limited this morning, but I tried the rest.  I think that makes for a very good start.

[WAS]

I did some nice pearls for still shots. Used a coloured roughness.

[WAS]

i tried this in PT and SR and it doesn't work anymore in TG. Shame. So that' beautiful effect is gone.

Can take a look at what it did look like in whatever version here: https://planetside.co.uk/forums/index.php/topic,27490.msg273059.html

Sucks cause it was very realistic. The distort by normal cause colours to flip conforming to geometry and give a realistic look. Especially in my second attempt on that thread.

[René]

I took a stab at making an iridescent rock. It is far from perfect, more of a proof of concept. The disadvantage of this method is that there are faint specular lights in the shadow side as well, which is not correct.

Keep in mind that in your example the surroundings of the rock are black, which largely determines the effect.

[ares2101]

I took a stab at making an iridescent rock. It is far from perfect, more of a proof of concept. The disadvantage of this method is that there are faint specular lights in the shadow side as well, which is not correct.

Keep in mind that in your example the surroundings of the rock are black, which largely determines the effect.

Whoa, how'd you manage that?

[René]

Sorry I forgot to post the TG file 

[WAS]

If you mix metallic and fresnel (using their functions) and then set the Fresnel tint to 0.25-0.5 you can get less intense specular that hides the colour. Then you can just apply a reflection shader for the actual specular you want to be a white sheen (plus ray traced reflections if need be). I actually used a inverted (complement colour) colour map (of the fresnel/metallic) for the default shaders roughness too which really helped the colours pop.