The correct answer is - D. Diamonds form in talc under very high pressure.
Diamonds were formed in the mantle and very big depth from the surface of the Earth. They are delivered towards the surface of the Earth by deep-source volcanic eruptions that are producing the kimberlite and lamproite pipes that are sought after by diamond prospectors. The diamonds that come from these processes weathered and eroded and are parts of the sedimentary deposits, most commonly in talk deposits.