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| Sunday, 6 November 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Limestone : Popular material in architecture
However, it is a very heavy material. It is also quite expensive. Limestone was most popular in the early 20th and late 19th centuries. Limestone (CaCO3) is a sedimentary rock (discussed earlier in Geo Facts) composed of the mineral calcite (calcium carbonate). The primary source of this calcite is most commonly marine organisms. These organisms secrete (put out) shells that settle out of the water column and are deposited on ocean floors as pelagic (deep sea) ooze. Limestone makes up about 10 per cent of the total volume of all sedimentary rocks. All the different kinds of limestone can be divided into two groups. The first group includes limestone that formed almost completely without the aid of any organisms. This type of limestone is forced out of the solution when the water evaporates. Such evaporation takes place in the hot lagoons of many coral reefs, and in most shallow tropical seas. The high temperature causes the water on the surface to evaporate. A white "lime" mud is deposited on the bottom of the sea. This white mud slowly hardens into a light-coloured limestone with a fine grain and even layers. Chalk is a limestone that remained soft. When spring water evaporates on land, calcium carbonate forms a crust over moss, dead leaves, and the ground. It builds up a mound or terrace called tufa. Evaporation of water in limestone caverns forms another variety of limestone, called travertine, into stalactites and stalagmites (calcium carbonate deposits shaped like icicles and pillars respectively). The second group of limestone forms by the work of organisms. Many aquatic organisms draw calcium carbonate out of the water and use it to make their shells and bones. Oysters, clams, snails, corals, and sea urchins do this. When the animals die, the shells and bones are broken up by waves into shell and coral sand and mud. Many of the beaches on the Pacific Islands are made of such coral mud and sand. Most of the limestone layers on earth were once shell or coral sand and mud. A limestone called coquina, formed of shells and coral, occurs in Florida. It is used to make roads and buildings. Limestone makes an excellent building stone because it can be carved easily. Like sandstone, it can be cut any way without splitting. For this reason, both limestone and sandstone are often called freestone. Limestone is especially good for foundations and walls where a high polish is not needed. Quarries in Indiana produce about half the building limestone in the United States. Pure limestones are white or almost white. Because of impurities, such as clay, sand, organic remains and iron oxide, many limestones exhibit different colours, especially on weathered surfaces. Limestone may be crystalline, clastic (containing fragments), granular, or dense, depending on the method of their formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock. Chert or flint nodules (lumps) are common in limestone layers. Limestone is a parent material of mollisols. Though the limestone used for construction is good for humid climates, it is vulnerable to acids, making acid rain a problem when it occurs in places where limestone is used extensively. The acids in the water can wear away the details of statues and other art. Limestone is also used to manufacture quicklime (calcium oxide). Some factories use limestone to clean waste gases and water before releasing them into the environment. Limestone is also used to make lime and to smelt (heat and melt) iron ore. Fact file Family: Sedimentary Formation: Formed from dead sea creatures and some weathered rock. Texture: Variable - can be fine, medium or coarse(rough) grained. Colour: Grey, blue, white, cream. Uses: Cement. Making soil less acidic. Iron and steel making. Chemistry: Reacts with dilute acid by fizzing. Note: Often contains fossils. |
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Have you heard the word limestone? Or wondered what it is? Limestone is
especially popular in architecture, and many landmarks around the world
are made primarily of the material. Limestone is readily available and
relatively easy to cut into blocks or more elaborate carvings. It is also
long-lasting and stands up well to exposure. 
