The physical property denoting a mineral's tendency to crack along parallel planar surfaces is cleavage.

Here's a breakdown:

* Cleavage refers to the ability of a mineral to break along specific planes of weakness within its crystal structure. This results in smooth, flat surfaces.

* Fracture, on the other hand, describes how a mineral breaks in ways other than cleavage. This can be irregular, conchoidal (shell-like), splintery, or hackly.

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