Which statement differentiates primary diamonds and alluvial diamonds?

• A. Primary diamonds are in kimberlite pipes; alluvial diamonds are eroded and deposited in riverbeds.
• B. Alluvial diamonds are formed under pressure; primary diamonds are formed in surface sediments.
• C. Primary diamonds are synthetic; alluvial are natural.
• D. Alluvial diamonds require blasting; primary diamonds do not.

Answer: (A)

Diamonds exist in two broad settings: primary deposits and secondary (alluvial) deposits. Primary diamonds crystallize deep in the mantle under high pressure and are brought to the surface by kimberlite magmas, forming pipe-like concentrations where mining occurs. Alluvial diamonds, on the other hand, originate from erosion of those primary sources and are transported by rivers and streams, eventually settling in riverbeds or other placers where they can be mined as alluvial deposits. The statement captures this distinction: primary diamonds are found in kimberlite pipes, while alluvial diamonds are eroded and deposited in riverbeds. The other ideas don’t fit because alluvial diamonds are not formed under pressure in surface sediments, diamonds are natural (not synthetic), and alluvial deposits don’t require blasting as a defining feature.