Attached pictures are of a stone I discovered in our garden after receiving a load of landscape rock, believe they cam from Colorado.
This particular stone is shaped like a road apple left by a horse. It is domed with a flat side like, as I said, a road apple left by a horse. Some of the surfaces are similar to a hard gray shell; while those areas where the shell has broken away are loosely packed red, black and clear crystalyn material that crumbles easily from the stone with light touch of the finger.
Any ideas?