There are two types of sedimentary rocks: those that are precipitated chemically, such as limestone or chert; and those that are made up of mineral fragments that are lithified, or compacted, together. The latter are called detrital, or clastic, sedimentary rocks and are formed when mineral fragments settle out of water or air into layers. As more and more particles, or sediments, are deposited, the weight over time compresses the fragments together, solidifying them into rocks.
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