Here are some other terms you might hear:
* Cobbles: These are larger, rounded rocks that are typically found in rivers and streams.
* Pebbles: These are smaller, rounded rocks that are also common in rivers and streams.
* Gneiss: This is a type of metamorphic rock that is often found in riverbeds. It can be very smooth and polished due to the action of water.
The smoothness of these rocks comes from the process of abrasion. As water flows over rocks, it carries sediment that grinds against the rock's surface. This constant friction gradually wears down the rock, smoothing out its edges and giving it a polished appearance.
The type of rock and the length of time it has been exposed to water can affect the smoothness of the rock. For example, a rock that is made of a softer material will be smoothed more quickly than a rock that is made of a harder material.
