Shale is the parent rock. It is made up of clay minerals. Shale can metamorphose into slate, phyllite, schist or gneiss depending on the degree of heat and pressure. Slate is the least metamorphosed of this group. Meaning that it has been subjected to the least amount of heat and pressure (low-grade metamorphism). It is associated with regional metamorphism due to mountain building. Slate is foliated and when expertly “cut” by striking with a specialized tool, it easily splits into thin, flat, parallel sheets of stone. This along with its chemical inertness and thermal stability make slate useful for many purposes. It is used for roofing shingles, floor tiles, and pool tables.