What are the two types of rocks in which diamonds are formed?

Diamonds are primarily formed within the Earth's mantle under high-pressure and high-temperature conditions, typically associated with specific types of rocks. Peridotite and eclogite are the two types of ultramafic rocks that provide the necessary environment for diamond formation.

Peridotite, which is rich in olivine and pyroxene, is the dominant rock in the Earth’s upper mantle. It forms under conditions that allow for the generation of diamonds, which crystallize from carbon sources under extreme pressure.

Eclogite, on the other hand, is formed from the metamorphism of basalt and is characterized by its rich content of garnet and pyroxene. This rock type, also found in the mantle, is essential for the transportation of carbon and can lead to diamond formation through processes involving subduction zones where oceanic crust is pushed into the mantle.

The other options, such as granite, basalt, sandstone, limestone, shale, and slate, do not provide the necessary high-pressure, high-temperature conditions or the right chemical environment for diamond growth. Thus, peridotite and eclogite are specifically associated with the genesis of diamonds due to their geological formation and composition.