Diamonds, the hardest gemstone on Earth and a symbol of luxury, and graphite, the material used in ordinary pencils to write on paper โ both are made of the same chemical substance: pure carbon. The dramatic difference between them โ diamonds being extremely hard, shiny, and transparent; graphite being soft, black, and dull โ is solely due to how the same carbon atoms are arranged in different structures.
In diamonds, each carbon atom is bonded to four other carbon atoms in a three-dimensional structure called a tetrahedral lattice. Each bond in this lattice is very strong, and it is the overall three-dimensional strength that makes diamonds the hardest naturally occurring material โ according to the Mohs scale, diamonds have a perfect score of 10.
In graphite, carbon atoms are arranged in flat layers called graphene. In each layer, each carbon atom is bonded to three other carbon atoms forming a very strong hexagonal pattern. However, the bonds between these layers are very weak, allowing the layers to easily slide over one another โ this is why graphite feels smooth and is good as a lubricant, and why it leaves a mark on paper when pressed.
Under extremely high temperature and pressure (approximately 1,000 degrees Celsius and pressure of 45,000-60,000 atmospheres), graphite can be converted into diamonds in a process used industrially to produce synthetic diamonds. Natural diamonds form deep within the Earth, about 160 kilometers below the surface, under suitable temperature and pressure conditions.