![]() Organic detrital rocks form when parts of plants and animals decay in the ground, leaving behind biological material that is compressed and becomes rock. The other is chemical rock, produced from the dissolution and precipitation of minerals.ĭetritus can be either organic or inorganic. The first is detrital rock, which comes from the erosion and accumulation of rock fragments, sediment, or other materials-categorized in total as detritus, or debris. Sedimentary rocks can be organized into two categories. Finally, lithification is the process by which clay, sand, and other sediments on the bottom of the ocean or other bodies of water are slowly compacted into rocks from the weight of overlying sediments. For example, as a lake dries up over many thousands of years, it leaves behind mineral deposits this is what happened in California’s Death Valley. Precipitation is the formation of rocks and minerals from chemicals that precipitate from water. Precipitation and lithification are processes that build new rocks or minerals. These three processes create the raw materials for new, sedimentary rocks. With this process, water that is slightly acidic slowly wears away stone. Dissolution is a form of weathering-chemical weathering. Erosion and weathering transform boulders and even mountains into sediments, such as sand or mud. The most important geological processes that lead to the creation of sedimentary rocks are erosion, weathering, dissolution, precipitation, and lithification.Įrosion and weathering include the effects of wind and rain, which slowly break down large rocks into smaller ones. When we find evaporites, we can tell that we were probably in a hot and dry environment such as a desert playa.Sedimentary rocks are formed on or near the Earth’s surface, in contrast to metamorphic and igneous rocks, which are formed deep within the Earth. So, when we find a limestone, we know that there was a large lake or ocean present at that location in the past. ![]() Limestones can also form from the shells of different sea critters that settle out on the bottom of the ocean. When this happens, the calcium carbonate is precipitated out of the water as calcite, forming limestone. For example, when cold sea water heats up, it can no longer hold as much calcium carbonate (calcite, the mineral that limestones are made out of) in solution. Limestones commonly form in oceans, which do not evaporate away. This is how rocks such as limestones form. They are typically made up of the minerals halite (calcium chloride, or rock salt) and gypsum (calcium sulfate).Īnother way to precipitate minerals out of water is to change the temperature (or the acidity) of the water rather than evaporate the water. ![]() ![]() This is a common way for chemical sedimentary rocks to form and the rocks are commonly called evaporites. At this point, as the water continues to evaporate, the salt will come out of solution and will be precipitated in the glass. As the water evaporates, the concentration of salt gets higher and the water will eventually become saturated and will not be able to dissolve any more salt. If you set the water in a hot and dry place (like Arizona) the water, but not the salt, will evaporate away. Precipitation is when dissolved materials come out of water.įor example: Take a glass of water and pour some salt (halite) into it. Chemical sedimentary rocks form by precipitation of minerals from water.
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