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Calcite: calcite forms and is stable at the Earth's surface. Some calcite is formed from precipitation, but much of the calcite in sedimentary rocks is formed by biological activity. Many marine organisms secrete skeletal material (shells) of calcite.In addition to these three most abundant minerals, some sedimentary rocks also contain the iron oxides hematite and limonite, and small amounts of feldspars and micas.any marine organisms secrete skeletal material (shells) of calcite. In addition to these three most abundant minerals, some sedimentary rocks also contain the iron oxides hematite and limonite, and small amounts of feldspars and micas.
Sedimentary rocks are formed from grains of minerals and rocks, dissolved minerals and other material, such as plant matter or animal remains, which have been transported and deposited as sediment.lant material can be found as fragments in sandstones or other sedimentary rocks, and if it makes up the bulk of the rock it is termed coal. The shells of many marine organisms are made of calcium carbonate, and form limestone or calcite-rich sediments such as marl (a calcareous mudstone).