Let’s take a look at how diamonds are formed over thousands of years, before they even get set into your 1 1 4 carat diamond ring. Normally, diamonds are formed under extreme pressure and temperature, at a depth of 125-200km inside the Earth’s mantle. It takes about 1 to 3 billion years for this to happen. The molecular structure of carbon gets altered into a compressed lattice structure. These lattices are called rough diamonds and are the purest form of diamond. Due to the changes they undergo, diamonds have the highest hardness of any known substance, as well as high thermal conductivity. Rough diamonds, after being formed, are carried to the surface of the Earth through volcanic eruptions originating at the depth of formation of the diamond. Since this is around 150 km or more, it happens very rarely. The diamonds carried to the surface come usually inside a greenish rock called kimberlite. This rock plays the role of the carrier for the diamond during eruptions.