The cracks along flat rock surfaces are called fractures.

Here's a breakdown:

* Fractures are breaks in the rock that don't involve movement along the break. They are common in rocks of all types, and can form from various processes like:

* Stress: Pressure from tectonic shifts or weight of overlying rock.

* Cooling: Rapid cooling of molten rock (like in volcanic flows).

* Weathering: Freeze-thaw cycles or chemical weathering.

While "cracks" is a common term, it's more accurate to use fractures when discussing geological features.