What is Limestone?
CHEMICALLY AND BIOCHEMICALL DEPOSITED SEDIMENTARY ROCKS The rocks described under this heading are, with a few noted exceptions, made up either completely or largely of materials that have been formed by chemical precipitation (in some cases as a result of evaporation), by biochemical precipitation, or by flocculation of colloidal suspensions. Chemical precipitation occurs when a solution becomes super saturated with a substance because of a change in the chemical properties of the solution Evaporation, when extensive, frequently causes solution concentrations that promote precipitation. Biochemical precipitation is precipitation that takes place either directly or indirectly in response to chemical activities of living organisms. Flocculation is the process whereby colloids, which are essentially molecular sized particles in suspension, are deposited, generally as gels that may be desiccated to solid masses of micro or cryptocrystalline substance. As already stated in the section deal
Limestone The rock forming the earths crust falls into three generic groups: igneous, sedimentary and metamorphic. Heat, pressure, and chemical reactions may change either igneous or sedimentary rock into metamorphic rock, meaning changed in form usually into more compact and crystalline condition, and even metamorphic rocks may be further altered to higher ranks of metamorphism. Rocks may become plastic under great pressure and high temperature and by earth movement. They may be folded into complex forms with a banded structure. Many Constituent minerals may be dissolved, transported, and reprecipitated by thermal waters. Heat and pressure may cause recrystallization. Limestone is defined as a rock of sedimentary origin composed principally of calcium carbonate or the double carbonate of calcium and magnesium, or a combination of these two minerals.
Limestone is a sedimentary rock composed of the mineral calcite (calcium carbonate). The primary source of this calcite is usually marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze (see lysocline for information on calcite dissolution). Secondary calcite may also be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems such as stalagmites and stalactites. Limestone makes up approximately 10 percent of the total volume of all sedimentary rocks. Pure limestones are white or almost white. Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces. Limestone may be crystalline, clastic, granular, or dense, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock. Che
Limestone is a type of sedimentary rock found in deposits all over the world and used in an assortment of ways. This rock is one of the most common forms of sedimentary rock, with an estimated 10% of sedimentary rock worldwide being composed of limestone. There are a number of different forms of this rock which come in an array of textures, colors, and appearances, and many people interact with products made from limestone on a daily basis. Like other sedimentary rocks, limestone is formed by the slow deposition of sediments, and their subsequent compression. The bulk of the world’s deposits are marine in origin, consisting primarily of the remains of plants and animals, including reefs, which were gradually deposited on the ocean floor and later compressed due to geological activity and the weight of subsequent layers of debris and the ocean itself. Limestone can also form very slowly through a process of leaching through mineral fields and deposition, as in the case of stalactites an
