Define: alluvial deposit.

Define: alluvial deposit.

• A. A deposit formed by meteorite impacts
• B. A deposit of volcanic glass near lava flows
• C. A deposit where gems are eroded from their source rock, and then transported away from the source and further concentrated
• D. A mineral-rich rock formed by crystallization deep underground

Answer: (C)

Alluvial deposits are sediments laid down by running water after material is eroded from its source rock and transported downstream. In gem contexts, gems are released by weathering, carried by streams, and concentrated where the current slows, such as in river bends, bars, or floodplains, forming placer-type accumulations. This water-driven transport and downstream concentration is the defining trait of alluvial deposits. Deposits formed by deep underground crystallization or by volcanic glass near lava flows come from different processes, and meteorite or impact-related deposits involve other origins.

Alluvial deposits are sediments laid down by running water after material is eroded from its source rock and transported downstream. In gem contexts, gems are released by weathering, carried by streams, and concentrated where the current slows, such as in river bends, bars, or floodplains, forming placer-type accumulations. This water-driven transport and downstream concentration is the defining trait of alluvial deposits. Deposits formed by deep underground crystallization or by volcanic glass near lava flows come from different processes, and meteorite or impact-related deposits involve other origins.