3D photogrammetry scan of a black & green ammonite fossil.
https://en.wikipedia.org/wiki/Ammonoidea
Three versions of the model in OBJ and FBX format are provided with 9k, 36k and 581k polys and each have 8k texture and normal maps and 4k occlusion maps.
Also included are STL files of 36k and 581k polys for 3D printing.