It is surely easy to do that, project all points on plane XY and then make a Convex 3d hull
I used my Nautilus plugin, but whatever convex hull tool will work (just input the points)
If you still want concavity and no overhang there could be others strategy to do so, by extruding the face for example and joining this extrusion to the block.
You can also sort rock positions with a stability criteria. My tool uses the biggest flat surface as first stable position, but you could calculate an angle of stability then choose the biggest or lowest one.