Here's why:
* Sedimentary rocks are formed from the accumulation and cementation of sediments. These sediments can be derived from the weathering and erosion of pre-existing rocks (clastic), or from chemical precipitation or biological processes.
* Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are subjected to heat and pressure, causing changes in their mineral composition and texture.
The size of the particles in a clastic sedimentary rock doesn't determine whether it's sedimentary or metamorphic. While very large particles might suggest a specific type of sedimentary rock (like a conglomerate), they don't change the rock's fundamental origin.
For example, a conglomerate is a type of clastic sedimentary rock composed of rounded pebbles, cobbles, or boulders. Even though the particles are large, the rock is still formed by the accumulation and cementation of sediments, which is the defining characteristic of sedimentary rocks.
