Here's why:

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

* Perfect cleavage means the mineral breaks cleanly and evenly along these planes.

* Three directions means the mineral breaks into smaller pieces that are all roughly the same shape, forming a rhombohedral shape.

Other minerals with good cleavage but not always perfect in three directions:

* Fluorite - Also has perfect cleavage in three directions, but it can sometimes be more conchoidal (curved) than perfectly flat.

* Galena - Has perfect cleavage in three directions, but it is sometimes described as cubic cleavage due to its tendency to break into cubes.

Let me know if you'd like to learn more about other minerals or their properties!