Alluvial diamonds are typically found in which environment?

• A. Off shore (boats, robotic crawlers)
• B. Onshore vacuum
• C. Rivers & streams
• D. Lamproite pipes

Answer: (C)

Alluvial diamonds sit in placer deposits formed by flowing water. Diamonds are very dense, so as rivers weather and erode their surroundings, the diamonds are carried downstream and tend to settle where the current slows, accumulating in gravels and sands along riverbeds and banks. This makes rivers and streams the typical environment where alluvial diamonds are found, since that’s where secondary, water-transported deposits form and concentrate. Lamproite pipes, by contrast, are primary source rocks where diamonds originate before being moved by erosion, not the alluvial setting. Offshore environments or an onshore “vacuum” aren’t the depositional environments for these secondary, riverborne deposits.