沙滩上的沙都从海里来吗？一粒沙可能走过河流，也可能来自生物

Often starting thousands of miles from the ocean, rocks slowly travel down rivers and streams, constantly breaking down along the way. Once they make it to the ocean, they further erode from the constant action of waves and tides.

Sand forms when rocks break down from weathering and eroding over thousands and even millions of years.

Black sand comes from eroded volcanic material such as lava, basalt rocks, and other dark-colored rocks and minerals, and is typically found on beaches near volcanic activity.

The fish bite and scrape algae off of rocks and dead corals with their parrot-like beaks, grind up the inedible calcium-carbonate reef material (made mostly of coral skeletons) in their guts, and then excrete it as sand.

Bermuda's preponderance of pleasantly pink beaches results from the perpetual decay of single-celled, shelled organisms called foraminifera.

百慕大只是粉红沙来源的一个实例，不能外推所有粉红沙滩。