What is Limestone

Limestone is a hard sedimentary rock, composed mainly of calcium carbonate i.e. CaCO3 or dolomite, used as building material and in the making of cement. Limestone makes up about 10% of the total volume of all sedimentary rocks. Limestone may also form in both lacustrine and evaporate depositional environments. Pure limestone’s 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 is also the main way you get lime, which is one of the things you make cement out of. To get lime, you have to burn limestone in lime kilns, and then what is left is lime.

Mainly limestone is composed from skeletal fragments of marine organisms such as coral or foraminifera. Limestone is an organic, sedimentary rock. This means it was formed from the remains of tiny shells and micro-skeletons deposited on the sea bed. With the passage of time they were compressed to form solid rock.

Bands of limestone emerge from the Earth’s surface in often spectacular rocky outcrops and islands.

The world’s largest limestone quarry is at Michigan Limestone and Chemical Company in Rogers City, Michigan.


Limestone is made up of calcium carbonate and reacts with diluted hydrochloric acid. Limestone is formed in layers – called bedding planes. These bedding planes contain vertical cracks called joints. Joints and bedding planes make the rock permeable.

The prime mineral or chemical compound present in limestone is calcium carbonate, but the rock is often mixed with other mineral impurities. These impurities can alter the texture of the rock, and also its colour. As an example of the diversity of limestone, both chalk and marble are forms of limestone, even though these two rock varieties look and feel very different.


Limestone is quarried for roadbeds, building and landscape construction, and cement manufacture. Limestone is very common in architecture. Its traces can be seen in history. Many landmarks across the world, including the pyramids in Egypt, are made of limestone. It is long-lasting and stands up well to exposure. However, it is a very heavy material, making it impractical for tall buildings, and relatively expensive as a building material. Limestone was most popular in the early 20th and late 19th centuries. Train stations, banks and other structures from that era are normally made of limestone.


Some varieties of limestone perform well in these uses because they are strong, dense rocks with few pore spaces. These properties enable them to stand up well to abrasion and freeze-thaw. Although limestone does not perform as well in these uses as some of the harder silicate rocks it is much easier to mine and does not exert the same level of wear on mining equipment, crushers, screens and the beds of the vehicles that transport it. Some additional but also important uses of limestone include:

Dimension Stone: Limestone is often cut into blocks and slabs of specific dimensions for use in construction and in architecture.

Roofing Granules: Crushed to a fine particle size, crushed limestone is used as a weather and heat-resistant coating on asphalt impregnated shingles and roofing.

Flux Stone: Crushed limestone is used in smelting and other metal refining processes. In the heat of smelting, limestone combines with impurities and can be removed from the process as a slag. Portland Cement: Limestone is heated in a kiln with shale, sand and other materials and ground to a powder that will harden after being mixed with water. Lime: If calcium carbonate (CaC03 is heated to high temperature in a kiln the products will be a release of carbon dioxide gas (CO2) and calcium oxide (CaO). The calcium oxide is a powerful acid neutralization agent. It is widely used as a soil treatment agent (faster acting than aglime) in agriculture and as an acid neutralization agent by the chemical industry.