This is a paid asset, but now you can download Rock Cliff Free.
Detail this asset from Unity Store: Original Link
Rock Cliff v3.0 (Latest version)
Features:
This is a photo real rock surface that could be seamlessly tiled horizontally. It could also be rearranged seamlessly in many ways, for example by duplicating the geometry and modifying it, adding deformers like “bend” or braking it down to several smaller elements and rearrange them in different ways.
Usage:
This geometry is meant to be used with a self-illuminated shader also known as a “surface shader”, “unlit shader” or an “emission shader” regardless if its used for films or games. Ideally you should choose the right balance of how much the geometry is being affected by lights in the scene versus how much it’s self-lit by its diffuse texture.