About
Limestone
Limestone is a sedimentary
rock composed largely of the mineral calcite which is a form of calcium
Carbonate (CaCO3). Limestones often contain variable amounts of
silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules,
or layers within the rock. The primary source of the calcite in limestone is
most commonly marine organisms. These organisms secrete shells that settle out
of the water column and are deposited on ocean floors or conglomerated in a
coral reef. Secondary calcite may also be deposited by supersaturated meteoric
waters (i.e. groundwater that precipitates the material in caves). Limestone
makes up about 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 colours, especially on weathered surfaces. Limestone may be
crystalline, clastic, granular, or massive, depending on the method of
formation.