Calcite will cleave according to it's rhombohedral shape. Of course weathering and abrasion can "round" or otherwise obscure the crystal form, but on a fresh face, calcite (and other such minerals) will cleave to their original form. Note the following:
The smaller piece that has broken away from the main crystal still retains the rhombohedral shape.
In this aggregate, if we looked at the individual crystal, we would see the unmistakable calcite rhombs.