Most of the diamonds are formed beneath the Earth at depths between 87 to 118 miles. The magma from volcanic eruptions carries these diamonds from the beneath of the Earth to the surface. These gemstones are actually hidden under igneous rocks, which are formed due to the cooling of the magma.
The oldest naturally occurring diamonds that are available in the market is estimated to be around approximately 4 billion years old. However, the age of most diamonds is estimated to be in between 1 billion to 3.3 billion years old.
Several diamond ring manufacturers believe that carbonado diamonds, which are mostly found in South America and Africa, was actually deposited by an asteroid, which ended up on the surface of the Earth about 3 million years ago.