Which statement best summarizes the formation conditions for diamonds as described?

Which statement best summarizes the formation conditions for diamonds as described?

• A. They form at shallow depths under low temperatures
• B. They form at depths around 140-220 km with carbon available
• C. They form only in subduction zones
• D. They form near the surface in volcanic rocks

Answer: (B)

Diamonds crystallize deep in the Earth's mantle where pressures and temperatures are extremely high, at depths roughly 140–220 kilometers, provided there is carbon available in the surrounding rocks. Under these conditions, carbon atoms can rearrange into the diamond lattice instead of graphite, forming a stable diamond phase. This mantle setting is essential; shallow depths or low temperatures do not favor diamond formation, and diamonds are not formed only in subduction zones nor right at the surface in ordinary volcanic rocks. They are carried upward to the surface by deep-sourced magmas like kimberlites, but the actual formation happens deep down where the necessary pressure and carbon are present.

Diamonds crystallize deep in the Earth's mantle where pressures and temperatures are extremely high, at depths roughly 140–220 kilometers, provided there is carbon available in the surrounding rocks. Under these conditions, carbon atoms can rearrange into the diamond lattice instead of graphite, forming a stable diamond phase. This mantle setting is essential; shallow depths or low temperatures do not favor diamond formation, and diamonds are not formed only in subduction zones nor right at the surface in ordinary volcanic rocks. They are carried upward to the surface by deep-sourced magmas like kimberlites, but the actual formation happens deep down where the necessary pressure and carbon are present.