Sedimentary rocks
Sedimentary rocks are one of the three main types of rocks. They make up around 3/4 of the rocks on Earth. They form on the Earth's surface in places like beaches, rivers, oceans and anywhere else where mud, sand or other types of sediment are collected. Sedimentary rocks preserve a record of the environments which existed when they first formed. Therefore, scientists can figure out how the climate and environments has changed throughout the Earth's history, by looking at different aged rocks. Many sedimentary rocks are made from bits and pieces of other rocks. these types are called clastic sedimentary rocks. The broken bits of the rocks are called sediment. the sediment will eventually form rocks when the little pieces get cemented together. Some sedimentary rocks, however are not formed from broken rock fragments. These are called chemical sedimentary rocks. They are made up of mineral crystals, such as halite and gypsum, and are formed by chemical processes. Other sedimentary rocks are made of the remains of living things such as clamshells, plankton skeletons, dinosaur bones and plants. these types are called organic sedimentary rocks.
Examples of Sedimentary Rocks
Examples of Sedimentary Rocks
- Conglomerate - Made up of round pebbles cemented together
- Breccia - Made up of angular pebbles cemented together
- Sandstone - Made of sand grains cemented together into solid stone.
- Selenite - Is an evaporate made of calcium sulfate that has many forms. Clear flattened crystals are called selenite. Satin spar and alabaster are also common forms.
- Halite - Is made when a body of seawater becomes closed off and evaporates. As the water evaporates it the remaining water can no longer hold the same amount of salt. The salt precipitates out and is deposited as crystallised halite or rock salt.
- Limestone - Is made primarily of calcium carbonate or calcite. The most common source of this calcite is the shells of marine organisms.