When shale is exposed to slight heat and pressure, it transforms into a slate.

Slate is a fine-grained, foliated metamorphic rock that exhibits a distinct planar structure, often referred to as "slaty cleavage". This cleavage allows the rock to break along smooth, parallel planes.

Here's a breakdown:

* Shale: A sedimentary rock composed of fine-grained clay minerals.

* Slight Heat and Pressure: These conditions are sufficient to cause the clay minerals to recrystallize and align themselves in a parallel arrangement.

* Slate: The resulting foliated metamorphic rock with a distinct cleavage.

Further increases in heat and pressure would transform slate into other foliated metamorphic rocks like phyllite, schist, and gneiss.