Limestone is one of the most versatile stones available to us. Limestone is a sedimentary rock, and its primary ingredient is calcium carbonate (CaCaO₃). Limestone ordinarily is white, but can appear in different colors and patterns due to impurities. Impurities of iron oxide gives the rock brown, yellow, or red color. Impurities of carbon can give it a blue, black, or gray color. The texture of this stone can be coarse to fine. Limestone mostly is more expensive than marble or granite rocks. As already mentioned above, limestone primarily consist of calcium carbonate in the form of the mineral calcite. Mostly, limestone is formed and found in clear, shallow, warm marine waters. Limestone is usually an organic sedimentary rock, which forms from the accumulation of shell, coral, algal, and fecal debris. Limestone can also get formed due to the precipitation of calcium carbonate from lake or ocean water. Limestone is found in shallow water areas, between 30 degrees north latitude and 30 degrees south latitude. It is found in the regions of the Caribbean Sea, Indian Ocean, Gulf of Mexico, Persian Gulf, around the Pacific Ocean islands, and within the Indonesian archipelago. Chalk: Chalk is very fine and soft in texture, and usually white or light gray in color. It is formed by the calcareous shell remains of very small marine organisms. Tufa: This type of limestone is produced by precipitation of calcium laden waters at a hot spring, near a lake, or other water body location. Fossiliferous: This limestone is abundant in fossils, which are the shell and skeletal fossils of organisms. Hence this type is called fossiliferous limestone. Shelly: This is basically a highly fossiliferous type of limestone. It is composed of many corals, mollusks, sponges, etc. The physical attributes of this limestone keeps varying according to the types of fossilized organisms present in it. Oolitic: This limestone is composed mostly of oolites, which are small spherical objects that are formed by the concentric precipitation of calcium carbonate on surface of sand grains. Travertine: This limestone is light in color, and gets deposited due to surface water and solution in ground. If it is porous it's called tufa, but when it is compact, it can be polished and is called onyx marble. Coquina: This poorly cemented limestone, is made of broken shell debris. It often forms on beaches, where waves segregates shell fragments of similar size. Lithographic: This is a dense limestone which is made of very fine and uniform grain. During the late 1700s lithography, which is a printing process was developed to reproduce images, by drawing images on stone with an ink, and then these stones were used to make multiple copies. Pisolitic: It is white or yellow in color. It is made of pisolites, which are small spherical bodies of calcium carbonate. It occurs due to precipitation of calcite and other minerals from turbulent and warm water Most of the limestone uses, can be attributed to the distinguishing limestone rock properties, which are its good hardness level, and its chemical property of being readily dissolvable in certain materials. Here are some facts about limestone and its uses. » Limestone is cut into blocks and used for construction and in architecture. It is used for making facing stone, floor tiles, window sills, stair treads, etc. » It is also used as a flux stone, where it is used in smelting and other metal refining processes. » Fine crushed limestone is used for making weather and heat resistant roofing. » As lime is an acid neutralizing agent, it is used as a soil treatment agent in agricultural practices. » Pulverized limestone is sprayed on the walls of the mines, so that it reduces the chances of explosion. The white color of the powder also helps in illumination. » Limestone is also used to make Portland cement, and used for various constructions. » Calcium carbonate is given to chicken and cattle as a dietary supplement. » The stalactites (hanging cylindrical structures from the roof) and stalagmites (cylindrical structures sticking up from the floor) observed in caves are made of limestone. When the water leaves the cave it leaves limestone behind, which leads to formation of these interesting structures. This process takes thousands of years. » Caves are formed due to various geologic processes, but most of them are formed in limestone due to dissolution process. » The caves found in areas which are rich in limestone can collapse, and when this happens a sinkhole is formed. » Just like the Great Pyramid, there are many monuments which are made of limestone. Some examples of such structures are The Cudgel of Hercules, La Zaplaz formations, Portland Stone quarry, etc. You can create your own limestone too. Here is a simple experiment that you can follow. Take an old cardboard box and line it snugly with plastic wrap. Add dry plaster, pieces of shells, and water in the box. Mix everything well. Then pour the mix in paper cups. Keep the cups for a week in a place where they don't get disturbed, like a cabinet. After a week remove the limestone mixture from the cups. Observe the texture, color, shape, and size of the limestones. To get a closer look at the types of limestone and other types of rocks, you can buy a rock and mineral kit. These kits come with a collection of 20, 50, or more rocks. You can observe the rocks minutely with the helps of these kits. Such kits are available online. Limestone has many other uses. Limestone is one of the most versatile among rocks due to its uses, and hence is used for making the houses we live in to a piece of chalk stick that we use for writing.