Here's a quick test using rocks from Bryce6 - the material is Waterline Moss from Stones/Rocks in Bryce6 but so long as you use the same material for all the rocks in the stack it should be fine.

If you make sure all the rocks are Positive in the 'A'tributes when they arrive you can then group them, then collapse them, and then you can export the mesh to say Wings3D and poke and prod at it in there until you get exactly the shape you want.

Measure your mind's height
by the shade it casts.
Robert Browning (Paracelsus)

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