All refraction heavy scenes like this take a certain degree of sampling to look good, expect some rendertimes for clean results. For real time engines this is of course not the case.

This scene has displacement activated on 4 objects (stones and demo sphere), should you not be able to render it directly, try to hide away displaced geometry until it is working for you.

Displacement is not needed, for the two included stones I added baked normals as well.

The included procedural displacement shader is working on generated UVs, so you should be able to use it on every surface that displaces well. If you are unsure how Cycles displacement is working please have a look around there are tons of free and professional tutorials out there.

Enjoy rendering!