Limestone is a sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3). The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record. Calcium (along with nitrogen, phosphorus, and potassium) is a key mineral to plant nutrition: soils overlying limestone bedrock tend to be pre-fertilized with calcium. Limestone is an important stone for masonry and architecture, vying with only granite and sandstone to be the most commonly used architectural stone. Limestone is a key ingredient of quicklime, mortar, cement, and concrete. The solubility of limestone in water and weak acid solutions leads to important phenomena. Regions overlying limestone bedrock tend to have fewer visible groundwater sources (ponds and streams), as surface water easily drains downward through cracks in the limestone. While draining, water slowly (over thousands or millions of years) enlarges these cracks; dissolving the calcium-carbonate and carrying it away in solution. Most well-known natural cave systems are through limestone bedrock.
Uses
Limestone is very common in architecture, especially in North America and Europe. Many landmarks across the world, including the Great Pyramid and its associated Complex in Giza, Egypt, are made of limestone. So many buildings in Kingston, Ontario, Canada were constructed from it that it is nicknamed the 'Limestone City'. [7] On the island of Malta, a variety of limestone called Globigerina limestone was for a long time the only building material available, and is still very frequently used on all types of buildings and sculptures. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving. It is also 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 late 19th and early 20th centuries. Train stations, banks and other structures from that era are normally made of limestone. Limestone is used as a facade on some skyscrapers, but only in thin plates for covering rather than solid blocks. In the United States, Indiana, most notably the Bloomington area, has long been a source of high quality quarried limestone, called Indiana limestone. Many famous buildings in London are built from Portland limestone.
Limestone was also a very popular building block in the Middle Ages in the areas where it occurred since it is hard, is durable, and commonly occurs in easily accessible surface exposures. Many medieval churches and castles in Europe are made of limestone. Beer stone was a popular kind of limestone for medieval buildings in southern England.
Limestone and marble are very reactive to acid solutions, making acid rain a significant problem. Many limestone statues and building surfaces have suffered severe damage due to acid rain. Acid-based cleaning chemicals can also etch limestone, which should only be cleaned with a neutral or mild alkaline-based cleaner.
Other uses include:
- The manufacture of quicklime (calcium oxide) and slaked lime (calcium hydroxide);
- Cement and mortar;
- Pulverized limestone is used as a soil conditioner to neutralize acidic soil conditions;
- Crushed for use as aggregate—the solid base for many roads;
- Geological formations of limestone are among the best petroleum reservoirs;
- As a reagent in desulfurizations;
- Glass making, in some circumstances;
- Added to paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler.
- Toothpaste
- Suppression of methane explosions in underground coal mines
- Added to bread and cereals as a source of calcium
