Limestone and sandstone are found in very large amounts all around the globe. They are common sedimentary rocks. However, their composition, origin and other properties of these two are different, making them unique.
Limestone is commonly found in marine-based environments, and they are classified as sedimentary type rocks. These are formed in shallow, warm and calm waters. Biological activity can also play an important role in the forming limestone. Normally, they are formed in waters where carbon dioxide concentration is low so that the sedimentation is quite easy. Marine water takes calcium from the land. There is lots of calcium carbonate containing materials, such as shells of molluscs and other sea based animals, coral, skeletal structures of sea animals, etc. When these are accumulated in the form of calcite, they are known as limestone. They are also categorised as biological sedimentary rocks.
There is another type of limestone known as chemical sedimentary rocks. They are formed by the direct precipitation of calcium carbonate in the sea. However, the biological sedimentary rocks are more abundant than chemical sedimentary rocks. In pure limestone, only calcite is located there, but often they can contain many impurities by mixing other materials like sand. So, limestone can be defined as a sedimentary rock, containing more than fifty percent of calcium carbonate in the form of calcite. Other than in the seas, limestone can also be formed in lakes or other water bodies with necessary conditions. In the Globe, limestone formation can be seen in Indian Ocean, Persian Gulf, Caribbean Sea, Gulf of Mexico, around the Pacific Ocean islands.
The nature of limestone depends on how it is formed in the first place. They can be in massive sizes, crystalline, granular, etc. They are classified into several groups according to their type of composition, formation or appearance. There are many classifications too. Some of the common limestone’s are coquina, chalk, lithographic limestone, fossil ferrous limestone, etc. There are many usages of limestone too. They are commonly used as an ingredient for cement and glass manufacturing. Since, limestone has a basic nature; it is used to neutralise acidic water bodies.
Sandstone is also a widely found sedimentary rock. It is formed in many environments such as lakes, oceans and deserts. They are mostly formed by sand grains and contain quartz in high quantities. Sandstone formation takes place in, Sahara desert in Central Australia, Africa, Arabian deserts, Western United States, etc. There can be types of sandstones in a variety of colours. Sandstones are used for cement or glass manufacturing. It has an aesthetic value, as well as an ornamental value. They can be cut, polished and then used as tiles or stylish rocks for buildings or as monuments.