Compare and contrast detrital and chemical sedimentary rock.

Let's start by looking at detrital sedimentary rocks. Detrital rocks are sometimes referred to as clastic sedimentary rocks because they are made up of clasts or rock fragments.

The word 'detrital' actually means 'rubbing away,' and we see that detrital rocks form when pre-existing rocks are rubbed away or weathered by forces such as water, ice and wind, leaving behind smaller rock fragments.

So, you can say that detrital sedimentary rocks are composed of rock fragments that have been weathered from pre-existing rocks. Because these rocks are created by the breakdown of other rocks, they are the most common rocks we see on the surface of the earth.

As these pieces of rocks get chipped away, they get carried by nature and roll and tumble and break up even more until they find a resting place in a low-lying area, like a valley or the basin of a lake or ocean where the grains of sediment accumulate and get cemented together, forming layers or strata. Sedimentary rocks are like clues that geologists use to piece together the past. For example, sedimentary rocks may hold fossils that reveal past life forms. These rocks can also contain cemented-together fragments of all different shapes and sizes that reveal bits of information geologists use to weave together the history of an area.

In this lesson, we will take a closer look at two types of sedimentary rocks: detrital, which contain these cemented rock fragments, and chemical, which, as you might guess, are rocks that form due to a chemical process.