Here's why:
* Organic sedimentary rocks are formed from the remains of once-living organisms like plants and animals. Think coal, limestone formed from shells, and oil shale.
* Clastic sedimentary rocks are formed from fragments of pre-existing rocks (igneous, metamorphic, or even other sedimentary rocks). These fragments are broken down by weathering and erosion, transported by wind, water, or ice, and then deposited and cemented together. Examples include sandstone, conglomerate, and shale.
So, while both types of sedimentary rocks are formed from fragments, the key difference is the source of the fragments: organic rocks from living things, and clastic rocks from broken rocks.
