Actually they were stone but *ssshh* x'D. That said I used a custom made lightbox with 4000K lightbulbs. I was also happy to find a function in 3dsmax -"Conform"- which conform/project a mesh onto an other. This way I can conform a geosphere to a cluster of rocks and then ending with a single complex mesh. I shared the process in a video you can watch on the next/previous post.
Later I released them with a 3rd version ( a smaller cluster) a better UVmapping, better LODs and less polygons.