Limestone is a sedimentary rock composed largely of the mineral calcite (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 as pelagic ooze or alternatively is conglomerated in a coral reef (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. Another form taken by calcite is that of oolites (oolitic limestone) which can be recognised by its granular appearance. Limestone makes up about 10 percent of the total volume of all sedimentary rocks.

PHYSICAL PROPERTIES OF LIMESTONE
Physically, Limestone are Quite impervious, Hard, Compact, fine to very fine grained calcareous rocks of sedimentary nature.
Hardness 3 to 4 on Moh's Scale
Density 2.5 to 2.65 Kg/m3
Compressive Strength 1800 to 2100 Kg/cm2
Water Absorption Less than 1%
Porosity Quite low
Weather Impact Resistant

CHEMICAL PROPERTIES OF LIMESTONE
Chemically, both limestone and marbles are siliceous calcium carbonate rocks.
Lime (CaO) 38-42%
Silica (SiO2) 20-25%
Alumina (Al2O3) 2-4%
Other Oxides like Na, Mg 1.5 to 2.5%
Loss On Ignition (LOI) 30-32%
Limestone, like marble and other calcareous stones, are referred to as acid sensitive. Calcareous stones are readily dissolved in acid, therefore acidic products should not be used on limestone and marbles.