Distinguish between chemically and organically formed sedimentary rocks.
Answers
Organic
Organic or biological sedimentary rocks are formed by living organisms, typically when the remains of living organisms build up and are compacted by sediment. Coal, for example, is made from long-dead vegetation crushed by thick layers of sediment and chemically altered through heat and pressure. Most limestone deposits are made from the shells of microscopic sea organisms. Coral reefs are a beautiful example of organic sedimentary rocks made by creatures that are still living -- corals that build their own homes from calcium carbonate.
Chemical
Chemical sedimentary rocks, by contrast, form when conditions favor a chemical reaction or process that causes chemicals dissolved in water to precipitate, creating a layer of sediment. When water in a salty sea or lake evaporates, for example, it may leave behind salt and gypsum deposits. In calcium-rich waters, changes in temperature or acidity may cause calcium carbonate to precipitate. Accumulation of calcium carbonate deposits can lead to the formation of limestone. Sometimes magnesium in water that enters the pores of a limestone rock can replace the calcium in the rock, turning limestone into another chemical sedimentary rock called dolostone.
Answer:
Clastic sedimentary rocks are made of sediments. The sediments differ in size. Chemical sedimentary rocks are made of minerals that precipitate from saline water. Organic sedimentary rocks are made from the bodies of organisms.