A diamond is neither igneous, metamorphic, nor sedimentary. Diamonds are formed deep within the Earth’s mantle under extreme pressure and high temperatures. They are brought to the surface through volcanic eruptions in a type of rock called kimberlite.
Diamonds are composed of carbon atoms arranged in a crystal structure. The process of diamond formation occurs at depths of about 140 to 190 kilometers below the Earth’s surface, where the conditions are suitable for carbon to crystallize into diamond.
In summary, diamonds are not classified as igneous, metamorphic, or sedimentary rocks. They are a unique mineral formed under specific geological conditions.