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Limestone

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Limestone is a sedimentary rock such as greater than 50% calcium carbonate ( calcite – CaCO3). There are many exceptional kinds of limestone formed thru a ramification of tactics. It may be precipitated from water ( non-clastic, chemical or inorganic limestone), secreted by using marine organisms including algae and coral (biochemical limestone), or can shape from the shells of lifeless sea creatures (bioclastic limestone). Some limestones form from the cementation of sand and / or mud by way of calcite ( clastic limestone), and these often have the appearance of sandstone or mudstone. As calcite is the precept mineral thing of limestone, it will fizz in dilute hydrochloric acid.

Colour: It can be yellow, white, or gray

Chemical Composition: Calcite

Texture – Clastic or Non-Clastic

Grain size – Variable, can consist of clasts of all sizes.

Hardness – Generally hard.

Clasts – if clastic / bioclastic then grains and / or broken or whole shell fragments visible; if non-clastic / chemical then crystalline and no clasts visible.

Major minerals: Calcite, dolomite

Type of Limestone

  • Bituminous limestone
  • Carboniferous Limestone
  • Coquina – A sedimentary rock that is composed mostly of fragments of shells
  • Coral rag
  • Chalk – A soft, white, porous sedimentary rock made of calcium carbonate
  • Fossiliferous limestone
  • Lithographic limestone
  • Oolite – Sedimentary rock formed from ooids
  • Rag-stone – Work done with stones that are quarried in thin pieces
  • Shelly limestone
  • Travertine – A form of limestone deposited by mineral springs
  • Tufa – Porous limestone rock formed when carbonate minerals precipitate out of ambient temperature water

Classification of Limestone

Two major classification schemes, the Folk and the Dunham, are used for identifying limestone and carbonate rocks.

Folk Classification

Robert L. Folk evolved a category gadget that places number one emphasis at the particular composition of grains and interstitial fabric in carbonate rocks. Based on composition, there are three most important additives: allochems (grains), matrix (often micrite), and cement (sparite). The Folk gadget uses -element names; the primary refers back to the grains and the second is the root. It is useful to have a petrographic microscope when using the Folk scheme, because it’s miles easier to determine the additives found in every pattern

Dunham Classification

The Dunham scheme specializes in depositional textures. Each call is based upon the feel of the grains that make up the limestone. Robert J. Dunham posted his system for limestone in 1962; it specializes in the depositional material of carbonate rocks. Dunham divides the rocks into 4 important corporations based on relative proportions of coarser clastic particles. Dunham names are essentially for rock families. His efforts cope with the question of whether or not or not the grains were at first in mutual contact, and therefore self-helping, or whether the rock is characterized by means of the presence of frame developers and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock. The Dunham scheme is more beneficial for hand samples due to the fact it’s far primarily based on texture, now not the grains inside the sample

Limestone Formation

Calcite, dolomite and aragonite are limestone minerals so where did they came from

It is a sedimentary rock. It forms predominantly on the sea floor where material rich in calcium carbonate (‘calcareous’ material) accumulates. This calcareous material may be organic, chemical or detrital in origin.

The sediment that goes to make up it may have been derived from the dead remains of marine organisms such as:

  • bryozoa
  • corals
  • crinoids
  • microscopic algae
  • shells

These organisms remove calcium carbonate (CaCO3) from the sea water to construct shells or skeletons.

CaCo3 cement, which may be fine grained (called micrite) or coarse grained (called sparite), holds the fossils (such as coccoliths and foraminifera) together to form a limestone.

Where is it found?

The development of the limestone market has been relatively fast in the Asia Pacific over the past decade, mainly due to the presence of developing countries in the region such as China, which holds maximum market share globally. Several countries in the Asia Pacific have witnessed rapid urbanization over the past few years, which has provided ample room for the expansion of the limestone market.

Europe also showed substantial growth. This region has a strong presence in the global steelmaking industry. Steel making requires large amounts of limestone as raw material, which is projected to drive the limestone market in the region during the forecast period. This rock market in North America is mainly driven by the need for it in agriculture and water treatment.

The market in Latin America is driven by demand for minerals in the agricultural industry, while building & building materials are the main applications of limestone in the Middle East & Africa. The increase in the incorporation of limestone in these two sectors is expected to drive markets in Latin America and the Middle East & Africa during the forecast period and in the future.

Limestone Characteristics and Properties

  • Stalactites and stalagmites in caves are leftover limestone that remains after water evaporates.
  • You will rarely find limestone in its pure white nature because it almost always has some impurities.
  • It can be found in just about any color depending upon which elements are combined with the calcium carbonate in the rock.
  • It is often used in construction such as being added to paint as a thickening agent.
  • When roofing styles have texture, it is normally because of crushed limestone being added to the roofing tar.
  • Animals can largely benefit from having limestone in their diet so it is often added to their feed.
  • It can most abundantly be found in the shallow ends of marine water.
  • Chalk is a type of limestone that contains mostly shells from marine animals.
  • During the 1700s, limestone was used for lithography which is when pictures are drawn on stones and then copied to other stones.
  • Because limestone contains the remains of dead organisms, it is considered an organic sedimentary rock.
  • There are rare chemical sedimentary rocks that form from the precipitation of calcium carbonate from ocean water.
  • Lithographic limestone is a type of limestone that contains fossils.
  • Powered limestone is used in coal mines as a safety precaution because it absorbs pollutants.
  • It can also be used on roofs to prevent or reduce weather or heat related roof damage.
  • Its turns into the metamorphic rock marble when subjected to high amounts of pressure and heat.

Limestone Uses

  • It is the raw material for the manufacture of quicklime (calcium oxide), slaked lime (calcium hydroxide), cement and mortar.
  • Pulverized limestone is used as a soil conditioner to neutralize acidic soils (agricultural lime).
  • Is overwhelmed to be used as aggregate—the strong base for many roads as well as in asphalt concrete.
  • Geological formations of limestone are most of the great petroleum reservoirs;
  • As a reagent in flue-gasoline desulfurization, it reacts with sulfur dioxide for air pollution manipulate.
  • Glass making, in some occasions, makes use of limestone.
  • It is added to toothpaste, paper, plastics, paint, tiles, and other substances as each white pigment and a reasonably-priced filler.
  • It can suppress methane explosions in underground coal mines.
  • Purified, it is delivered to bread and cereals as a supply of calcium.
  • Calcium levels in cattle feed are supplemented with it, together with for chicken (when ground up).
  • It may be used for remineralizing and increasing the alkalinity of purified water to prevent pipe corrosion and to repair important nutrient tiers.
  • Used in blast furnaces, limestone binds with silica and different impurities to remove them from the iron.
  • It is often located in medicines and cosmetics.
  • It is utilized in sculptures because of its suitability for carving.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing. Cite this article as: Geology Science. (2019). Limestone. [online] Available at: http://geologyscience.com/rocks/sedimantery-rocks/limestone/ [14th December 2019 ]
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