* Sedimentary Rocks: Formed from the accumulation and cementation of sediments, like sand, gravel, and the remains of organisms.

* Igneous Rocks: Formed from the cooling and solidification of molten rock (magma or lava).

* Metamorphic Rocks: Formed when existing rocks (igneous, sedimentary, or other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

River rocks are often fragments of other rocks that have been eroded, transported by water, and deposited in a riverbed. Over time, these fragments become rounded and smoothed by the water's action, creating the characteristic look of river rocks.