Limestone is a sedimentary rock, which means it was formed from small particles of rock or stone that have been compacted by pressure. Sedimentary rock is important because it often contains fossils and gives clues about what type of rock was on the Earth long ago.
what is limestone?
Limestone is a very common sedimentary rock consisting of more than 50% calcium carbonate(CaCO3) in the form of the mineral calcite. Although it occurs in many different forms, its origins can be traced back to either chemical or biochemical processes that occurred in the geological past, often tens to hundreds of millions of years ago.
It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal, and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.
Because limestone is often formed from shells and bones, it is a light color like white, tan, or gray. The color of the limestone depends on the other sediments in the mixture besides the mineral calcite, which is white; impurities such as sand, clay, and organic material are also present in limestone and affect the color.
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How is limestone Formed?
Limestone is formed in two ways. It can be formed with the help of living organisms and by evaporation.
Most limestones are marine deposits, but some are formed in lakes, rivers and on land.
Limestones consisting mainly of animal shells. The shells of many animals, those that live either in the sea or in freshwater, consist of calcium carbonate (calcite and aragonite). When the animals die, their shells are left on the ocean floor, lake bottom or river bed where they may accumulate into thick deposits.
- Crinoidal Limestones – Crinoids are sea animals that had long stems, cup like bodies and long filter arms, that look so much like flowers that they are call sea lillies. The stems breaks into small, disc shaped fragments. Some limestones of the Pennsylvanian and Permian aged rocks of Kansas contain so many of these stem fragments that the term crinoidal limestone describe them well. These are found extensively in eastern Kansas. The Cretaceous Niobrara Chalk is one of the few localities in western Kansas that contains beautiful specimens of stemless crinoids, in which both the bodies and the long arms are well preserved.
- Fusilinid Limestones – The Fusilinid is a member of the single-celled animals call Foraminifera. These small animals, whose shells look like grains of wheat, were abundant during the Pennsylvanian and Permian periods. Many limestone are almost solid masses of fusilinid shells.
- Reef-like Limestones and Shell Limestones-These limestones contain the remains of corals, brachipods, clams, oysters, bryozoans and other forms. Some of these animals lived on colonies and the remains formed lens-shaped or elongated deposits, which sometimes grew to several hundred miles in length. The ones found in Kansas are, however, much smaller. Reeflike bodies in eastern and southeastern Kansas were formed by limy mud trapped by leaf-like blades of marine algae. Small colonies or groups of fossil shells in some formations measure only a foot in diameter. Their biological origin is often revealed in the rock by the presence of fossils.
Today Earth has many limestone-forming environments. Most of them are found in shallow water areas between 30 degrees north latitude and 30 degrees south latitude. Limestone is forming in the Caribbean Sea, Indian Ocean, Persian Gulf, Gulf of Mexico, around Pacific Ocean islands, and within the Indonesian archipelago.
One of these areas is the Bahamas Platform, located in the Atlantic Ocean about 100 miles southeast of southern Florida. There, abundant corals, shellfish, algae, and other organisms produce vast amounts of calcium carbonate skeletal debris that completely blankets the platform. This is producing an extensive limestone deposit.
Limestone can also form through evaporation. Stalactites, stalagmites, and other cave formations (often called “speleothems“) are examples of limestone that formed through evaporation. In a cave, droplets of water seeping down from above enter the cave through fractures or other pore spaces in the cave ceiling. There they might evaporate before falling to the cave floor. When the water evaporates, any calcium carbonate that was dissolved in the water will be deposited on the cave ceiling. Over time, this evaporative process can result in an accumulation of icicle-shaped calcium carbonate on the cave ceiling. These deposits are known as stalactites. If the droplet falls to the floor and evaporates there, a stalagmite could grow upwards from the cave floor.
The limestone that makes up these cave formations is known as “travertine” and is a chemical sedimentary rock. A rock known as “tufa” is a limestone formed by evaporation at a hot spring, lake shore, or other area.
Types of limestone
Limestone is by definition a rock that contains at least 50% calcium carbonate in the form of calcite by weight. All limestones contain at least a few percent other materials. These can be small particles of quartz, feldspar, clay minerals, pyrite, siderite, and other minerals. It can also contain large nodules of chert, pyrite, or siderite. The calcium carbonate content of limestone gives it a property that is often used in rock identification – it effervesces in contact with a cold solution of 5% hydrochloric acid.
There are many different names used for limestone. These names are based upon how the rock formed, its appearance or its composition, and other factors. Here are some of the more commonly used varieties.
- Chalk: A soft limestone with a very fine texture that is usually white or light gray in color. It is formed mainly from the calcareous shell remains of microscopic marine organisms such as foraminifers, or the calcareous remains from numerous types of marine algae.
- Coquina: A poorly-cemented limestone that is composed mainly of broken shell debris. It often forms on beaches where wave action segregates shell fragments of similar size.
- Fossiliferous Limestone: A limestone that contains obvious and abundant fossils. These are normally shell and skeletal fossils of the organisms that produced the limestone.
- Lithographic Limestone: A dense limestone with a very fine and very uniform grain size that occurs in thin beds which separate easily to form a very smooth surface. In the late 1700s, a printing process (lithography) was developed to reproduce images by drawing them on the stone with an oil-based ink and then using that stone to press multiple copies of the image.
- Oolitic Limestone: A limestone composed mainly of calcium carbonate “oolites,” small spheres formed by the concentric precipitation of calcium carbonate on a sand grain or shell fragment.
- Travertine: A limestone that forms by evaporative precipitation, often in a cave, to produce formations such as stalactites, stalagmites, and flowstone.
- Tufa: A limestone produced by precipitation of calcium-laden waters at a hot spring, lake shore, or other location.
image source: http://www.sandatlas.org/limestone/
how was IT used THROUGHOUT history ?
Nobody knows exactly when humans first discovered lime. Perhaps ancient occupants of Earth used limestone rock to protect their fireplaces. Fire heated the rocks and the first burnt lime was created. It then rained and the lime slaked into calcium hydroxide, which reacted with the ashes and sand around the fireplace creating the first ancient mortar. Lime foundations in eastern Turkey show that this was already being used 14,000 years ago. Earlier still, the Lascaux caves in France feature frescoes of natural iron oxide pigments applied to damp cave walls of high calcium content (limestone) dating back as far as 16,000 years. Limestone has quite a history. Long ago, limestone was used to build the pyramids in Egypt. And Romans would mix limestone with volcanic ash to form a type of concrete for building structures in Rome.
Key dates of lime usage
- c. 7500 B.C. The ancient people who lived in the area that is now Jordan, made a plaster from lime and unheated crushed limestone to cover walls, floors and hearths in their homes.
- c. 3000 B.C. The Egyptians tanned their skin with lime and built one of the limestone wonders of the world; the 137 m high Cheops pyramid.
- c. 2800 B.C. – c. 1000 A.D. Celts fertilized fields with lime. Lime colors were featured in Greek frescos.
- c. 500 B.C. The Chinese built the 2,500 km Great Wall by stabilizing the soil with lime and used lime mortars to cement the stones together.
- c. 753 B.C. – 535 A.D. Roman frescos and buildings featured different lime colors. Women colored their hair to a light red hue with unslaked lime.
- c.400 A.D. – c. 1100 A.D. Alchemists discovered the caustic properties of lime and created a soap based on wood ash. The Lhoist logo recalls the alchemic symbol for lime.
- c. 1300 A.D. – c. 1800 A.D Lime was widely utilized throughout Europe as a plaster and paint décor, and it served as a principal building material for homes.
- 14th and 15th Centuries In southeast England, artisans applied decorative lime plaster to the exterior of timber-framed structures. During the Renaissance, lime made a revival in the plastering and painting arts.
- 16th Century Lime usage increased coincident with evolutions in building and construction, as new processes for creating different types of structures and finishes were developed.
- 17th Century The Scagliola technique came into fashion as an effective substitute for costly marble inlays. It comprised a pigmented mixture of lime dust, marble or scale. It was also used to create building facades, stucco columns, sculptures and other architectural elements that resemble marble.
- 18th& 19th Centuries Black and Lavoisier described the chemical reaction of lime. Debray and Lechatelier discovered others qualities and applications. For example, limestone was included for the first time as an ingredient in toothpaste.
- 20th and 21st Centuries The proliferation of new innovations, especially the birth and rapid development of technologies, broadened the use of lime. Today, we encounter lime or the results of treatments involving lime in one form or another at just about every minute of the day.
Because it is a softer stone, it is easily carved. Limestone appears in many buildings. Indiana limestone, also known as Salem limestone, can be found at the Empire State Building in New York City and on the U.S. Holocaust Memorial and Museum in Washington D.C.
where can IT BE fOUnd today?
Also important uses of limestone include:
- Dimension Stone: Limestone is often cut into blocks and slabs of specific dimensions for use in construction and in architecture. It is used for facing stone, floor tiles, stair treads, window sills, and many other purposes.
- Roofing Granules: Crushed to a fine particle size, crushed limestone is used as a weather and heat-resistant coating on asphalt-impregnated shingles and roofing. It is also used as a top coat on built-up roofs.
- Flux Stone: Crushed limestone is used in smelting and other metal refining processes. In the heat of smelting, limestone combines with impurities and can be removed from the process as a slag.
- Portland Cement: Limestone is heated in a kiln with shale, sand, and other materials and ground to a powder that will harden after being mixed with water.
- AgLime: Calcium carbonate is one of the most cost-effective acid-neutralizing agents. When crushed to sand-size or smaller particles, limestone becomes an effective material for treating acidic soils. It is widely used on farms throughout the world.
- Lime: If calcium carbonate (CaC03) is heated to high temperature in a kiln, the products will be a release of carbon dioxide gas (CO2) and calcium oxide (CaO). The calcium oxide is a powerful acid-neutralization agent. It is widely used as a soil treatment agent (faster acting than aglime) in agriculture and as an acid-neutralization agent by the chemical industry.
- Animal Feed Filler: Chickens need calcium carbonate to produce strong egg shells, so calcium carbonate is often offered to them as a dietary supplement in the form of “chicken grits.” It is also added to the feed of some dairy cattle who must replace large amounts of calcium lost when the animal is milked.
- Mine Safety Dust: Also known as “rock dust.” Pulverized limestone is a white powder that can be sprayed onto exposed coal surfaces in an underground mine. This coating improves illumination and reduces the amount of coal dust that activity stirs up and releases into the air. This improves the air for breathing, and it also reduces the explosion hazard produced by suspended particles of flammable coal dust in the air.
Limestone has many other uses. Powdered limestone is used as a filler in paper, paint, rubber, and plastics and as a sorbent (a substance that absorbs pollutants) at many coal-burning facilities . Crushed limestone is used as a filter stone in on-site sewage disposal systems.
image source: http://geology.com/usgs/limestone/
info sources: http://geology.com/rocks/limestone.shtml