What is the difference between primary and secondary diamond deposits?

• A. Secondary deposits are diamond-bearing material eroded from rocks and redeposited in rivers or sea beds.
• B. Primary deposits are formed by biological processes, while secondary deposits result from chemical weathering only.
• C. Primary deposits host diamonds within their original host rock (kimberlite), while secondary deposits are diamond-bearing material eroded from rocks and redeposited in rivers or sea beds.
• D. All diamonds come from secondary deposits.

Answer: (C)

Diamonds come from two related but distinct settings: where they crystallized and how they move after that. In a primary deposit, diamonds are still within their original host rock, typically a kimberlite pipe, meaning the diamonds formed deep in the mantle and are found ore-bearing right in the rock that brought them to the surface. In a secondary deposit, those same diamonds have been released from the host rock by erosion and weathering and then transported by water, settling out in placer environments like river gravels, beach sands, or seafloor sediments. The key idea is that the primary deposit shows the diamonds still in the original rock, while the secondary deposit shows diamonds that have been moved and redeposited after erosion.

This is why the best statement matches the concept: it correctly links primary deposits to diamonds remaining in their original kimberlite-host rock and secondary deposits to diamond-bearing material eroded from rocks and redeposited in rivers or seas. The other ideas mix up how diamonds form—biological processes don’t create diamonds—and misstate the relationship, since not all diamonds come from secondary deposits; many are discovered in primary kimberlite sources, and some diamonds are found only after primary rocks weather and release them into placer deposits.