What causes pressure that allows diamonds to form from the mantle?

Diamonds form in the Earth's mantle under extreme conditions of high pressure and temperature, typically at depths of about 150 to 250 kilometers. The immense pressure, often exceeding 725,000 pounds per square inch, is generated by the weight of the overlying rock layers and the dynamic processes occurring within the Earth's interior. Additionally, the presence of carbon sources, along with these conditions, facilitates the crystallization of carbon atoms into the structured lattice that characterizes diamond.