I do not like the Phong/2000exp bright new fully opaque RVB marbles :D

I experimented on v-ray a solution with Fresnel and SSS quite good enougth for vizualisation, but certainly not physical even if the BRDF is not so bad.

Find here an other experimentation with a bit more complexe material based on some specular, complex absorptions and a final vanishing coating. Much more physical if you excuse the RVB absortion maps! :)

[Requires Indigo 4]