Rocks (Book)

Over time, deposited sediments may harden into rock. First, the sediments are compacted. That is, they are squeezed together by the weight of sediments on top of them. Next, the sediments are cemented together. Minerals fill in the spaces between the loose sediment particles. These cementing minerals come from the water that moves through the sediments. These types of sedimentary rocks are called “clastic rocks.“ Clastic rocks are rock fragments that are compacted and cemented together.

Clastic sedimentary rocks are grouped by the size of the sediment they contain. Conglomerate and breccia are made of individual stones that have been cemented together. In conglomerate, the stones are rounded. In breccia, the stones are angular. Sandstone is made of sand-sized particles. Siltstone is made of smaller particles. Silt is smaller than sand but larger than clay. Shale has the smallest grain size. Shale is made mostly of clay-sized particles and hardened mud.