Here's why:

* Cleavage refers to the tendency of a mineral to break along specific planes of weakness.

* Rhombohedral cleavage means the mineral breaks into fragments that are shaped like rhombohedrons, which are six-sided figures with parallelogram faces.

* Calcite has a very distinct rhombohedral cleavage, making it relatively easy to identify.

Let me know if you have any more mineral questions!