This is a 3D scan I did on a little piece of rock, I think it can be a good base mesh to custom and rework to get rocks obviously and/or a terrain. The scan was made with MeshRoom and some modifications and the rendering on Blender, I provide besides .blend are the following formats : .abc, .dae, .usdc, .fbx, .glb, .obj, .ply, .stl and .x3d.

I give it as it came out of the scan, I just applied a collapse decimate modifier at different proportions (reduce the amount of vertices/faces), in the file you will find the original scan on the left and folllowing to the right 16 versions with the decimate modifier applied with those ratios : 0.75, 0.5, 0.25, 0.2, 0.15, 0.1, 0.05, 0.04, 0.03, 0.02, 0.01, 0.005, 0.004, 0.003, 0.002 and 0.001.

The original is 34 522 vertices and 68 438 polygons and the 0.001 decimate ratio is 61 vertices and 67 polygons, so you should be able to choose the amount of poly that match the best with your needs (details or performance).

Spaced out a bit further in the right still are 3 other version I applied a planar decimate to 3 of the ones that I already collapsed because I found the resulst was pretty cool giving a different style kind of more cubic, same as for the collapse at right are the lowest poly amount. For 1st it goes from 791 vertices and 983 polygons to 413 vertices and 194 polygons, for 2nd 224 vertices and 246 polygons to 132 vertices and 59 polygons and for 3rd 392 vertices and 361 polygons to 210 vertices and 79 polygons.

I am at your disposal if you have any question.

Thanks !