Industrial Minerals:
Limestone is a kind of rock made up of calcite which is a mineral form of calcium carbonate. All limestones are formed when the calcium carbonate crystallizes out of solution.
The first kind of limestones that formed without the help of organisms. This type of limestone is forced out of solution when the water evaporates due to the high temperature . A white “lime” mud is remained on the bottom of the lake/ocean. This white mud turns into a light-colored limestone with a fine particle and even layers after a long time. Chalk is a soft limestone.
Second kind of limestone is a calcareous sedimentary rock which is formed at the bottom of lakes and seas with the shells, bones of millenia old dead sea creatures and other calcium rich material. The fossil (shell, coral, algal, and fecal debris) upon which it settles layer after layer in lakes or ocean is piled up adding weight over thousands and millions of years. The heat and pressure causes chemical reaction at the bottom and the sediments turn into solid stone, the limestone. Limestone can also get formed due to the precipitation of calcium carbonate from lake or ocean water.
It is composed of calcium carbonate that is calcite (CaCO3). It is normally white however it might be found in different colors (such as blue, black, red, yellow, brown or gray) due to impurities of carbon and iron inside. The texture goes from fine to coarse.
Limestone that will take a polish are considered marbles by most people. However if there are still shells visible or the structure is not crystalline, it is still a limestone and it is more expensive than marble or granite rocks. A part of calcium molecules if being replaced by magnesium, it is known as magnesium lime stone or dolomite limestone.
If it contains more than 95% of calcium carbonate is known as high-calcium limestone. Recrystallised limestone takes good polish and is used as decorative and building stone.
Limestone makes an excellent building stone because it can be carved easily and be cut any way without splitting. Hence, both limestone and sandstone are often called freestone. Limestone is especially good for foundations and walls where a high polish is not needed.
Applications of Limestone
