A diamond is a precious stone and is the hardest naturally occurring material known. It is made from carbon which can come in different forms depending on how its atoms are arranged. A diamond has a lattice structure in which the atoms are bonded together very strongly.
Diamonds are formed deep underground in the earth’s mantle, around a 100 miles down. They are formed under high pressure and temperatures and can take 1 to 3 billion years to form. They are brought closer to the surface by deep volcanic eruptions and are then mined by people.
For a video explanation, please see below.