Slate is a metamorphic rock that forms from mudstone or shale. The mudstone or shale normally contains clay or volcanic ash. Slate is unique in that it does not require any type of cementation to hold its particles together.It has a very attractive appearance and it is also durable. Interesting Slate Facts:halk boards are made of slate and chalk is made of limestone, another type of rock. Slate is used to make turkey calls which are devices that mimic the sound of different turkeys and used by hunters. Slate has a wet-like appearance when exposed to the sun.