Crustal diamond forms where?

• A. A diamond formed only deep in the mantle.
• B. A rare diamond that forms in the continental crust at or near the earth's surface due to meteorite impact or tectonic plate collision.
• C. A synthetic diamond produced by surface treatments.
• D. A diamond formed in the oceanic crust near mid-ocean ridges.

Answer: (B)

Crustal diamonds form when rocks in the continental crust experience localized high-pressure, high-temperature conditions near the surface, typically during meteorite impacts or tectonic plate collisions. These events create pockets or veins where carbon can crystallize directly into diamond within crustal rocks, which is why such diamonds are rare compared with those formed deep in the mantle and brought toward the surface by magmatic processes. This makes the statement describing a rare diamond forming in the continental crust at or near the Earth's surface due to impact or plate collision the correct one.

The idea that diamonds form only deep in the mantle describes mantle diamonds, not crustal ones. Synthetic diamonds produced by surface treatments are man-made, not natural crustal diamonds. Diamonds formed in the oceanic crust near mid-ocean ridges would not reflect the typical crustal setup for natural crustal diamond formation in continental rocks.