Answer:
beneath the surface of Earth
Explanation:
Diamonds are made up of carbon that has been placed under extreme heat and pressure conditions.
These conditions of high pressure and temperature can only be found within the subsurface. As you go deeper to the mantle, the geothermal gradient rises significantly.
Also, the overburden pressure will also be high.
These processes can also occur on other planets and some can be associated to the earth times when the earth was being formed.
The condition at which diamond forms confers some of the distinct natural properties that typifies it.
