Scanned a real stone with FabScanPi.
Cleaned and simplified the scan with Meshlab.
Scaled (made more cubic) in blender.
In FreeCad I cut out a part, installed the cube and exported the STL for printing.
The first two photos show the "stone" casted in different types of concrete, the next one in chocolate ;)
I printed with 0.2 mm - execpt the medium sized (1:1) - this one was printed with 0.1 mm to make the surface smoother, cause this is the one I used to make the silicon casting form.