What type of rock turns into a diamond?

I'm curious to know, which kind of rock undergoes a transformation to become a sparkling diamond? Diamonds, renowned for their hardness and allure, must originate from some specific geological source. Are they formed deep within the earth's crust, perhaps under immense heat and pressure? Or do they originate from a more accessible, surface-level rock type? Could it be igneous rocks, sedimentary rocks, or metamorphic rocks? Each type of rock has its unique characteristics and formation processes. Could you enlighten me on this intriguing transformation from rock to diamond?