Materials/Structure

Diamonds are completely made from carbon, also known as C, well below the earth’s surface.  One carbon atom joins with four other carbon atoms by covalent bondage to form a diamond.  The chemical structure is made up of eight atoms and is arranged in a cube form. 

Molecular Structure of a Diamond

This structure is very stable, making diamonds hard, durable, and lasting. In fact, according to the MOHS Hardness Scale, diamonds receive a score of ten, meaning that they are the hardest gems. Diamonds have a refractive index of 2.42, a dispersion of 0.044, and a specific gravity of 3.52.  Additionally, uncut diamonds are generally found in cubic forms.   

So, if graphite is also completely made up of carbon, why it is rated as the softest material on the MOHS Hardness Scale.  Well, the carbon atoms in graphite form thin sheets of atoms, making graphite so soft. Even though diamonds and graphite are made up of exactly the same materials, the positioning and bonding of atoms make them completely different.