Limestone is a sedimentary rock made from calcite as a result of organic means or chemical means over a longer period of time. It’s a very useful material that is used for many applications. Limestone can be used in flooring, as different building materials, as additives to make cement and concrete, as well as many other applications. The reason that limestone is so useful stems from its physical and chemical properties.
While not nearly as durable or hard as granite, limestone is relatively hard with a hardness of 3 to 4 on the scale on the Moh’s scale. It has nearly the same density as granite which makes it sometimes difficult to use in some building applications as slabs of limestone are not easy to move around. Limestone is also not very porous and resistant to most weathering.
This makes it nearly identical to marble which makes sense as marble is created from limestone. Any limestone that can take a polish is actually considered marble. Limestone is sometimes preferred though as it is cheaper than either of its counterparts and much easier to cut than granite. The thermal expansion of limestone is not very large; in fact limestone aggregate in concrete shows less expansion than other types of aggregate. However at higher temperatures, limestone will begin to crack due to thermal expansion.
Limestone is primarily made of calcium containing material such as calcium oxide and calcium carbonate. About 38-42% of limestone is calcium oxide (CaO) while about 30-32% is carbonate containing compounds like calcium carbonate (CaCO3) or even magnesium carbonate (MgCO3). The remaining constituents are silica dioxide (SiO2) at 15-18%, Alumina (Al2O3) and between 1-3% of magnesium dioxide, iron oxides and other materials. Some limestone is very pure with just calcium containing compounds but most limestone has other constituents and is referred to a ‘dirty’ limestone.
While limestone has a good hardness and will resist most weathering it is one of several rocks, like marble, that are known as acid sensitive. In the presence of acid, these materials will begin to break down and readily dissolve in stronger acids. This also means that limestone will be affected by acid rain and material or sculpture that is composed of limestone or marble will suffer because of the interactions between the acid and the main constituents of the material.
As a material
The usefulness of limestone as a material is due to its properties. While limestone is not nearly as good as granite in terms of hardness and weather resistance, it is probably a just as good. Limestone is much cheaper and easier to obtain than granite and despite a somewhat lack of aesthetics in comparison to marble and granite, limestone has a much wider array of applications.