It used to be slate, but most modern black boards are wood particle board with a black paint like coating applied. This is cheaper and lighter as well as making bigger boards possible.
sedimentary rock can form rock such as sandstone that the Egyptian pyramids were built of or they can form the chalk that is used to write on the ground or on a black board.
slate
Basalt can be used for making roads
A black board is used as an instructional tool at the front of a classroom. A teacher uses a blackboard to write information about the subject they are teaching to a classroom.
Black Rock received its name from a large black volcanic rock formation located on its coast. This distinctive rock was used as a navigational landmark by early travelers in the area, leading to the area being known as Black Rock.
this rock is used for smelting and making glass
Chalk
because the particles of the chalk or any other substance which is used to write on black board has very tiny particles which get attached with white board.
Slate
Particle (MDF) board is used for making doors, partition & some furniture like shelves.
better chance of making a basket
The black board is known as such because in earlier times slate was used (which is black) instead of the "color green" stuff that you see now. The materials changed but the name stuck.