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limestone,sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine. Most limestones are formed by the deposition and consolidation of the skeletons of marine invertebrates; a few originate in chemical precipitation from solution. Limestone deposits are frequently of great thickness. The action of organic acids on underground deposits causes such formations as the Luray Caverns, the Carlsbad Caverns, and Mammoth Cave. Limestone is used as a flux in the extraction of iron, as an ingredient in Portland cement, as a source of lime (see calcium oxidecalcium oxide,
chemical compound, CaO, a colorless, cubic crystalline or white amorphous substance. It is also called lime, quicklime, or caustic lime, but commercial lime often contains impurities, e.g., silica, iron, alumina, and magnesia.
..... Click the link for more information. ), as a building stone, and for ornamentation. Among the important varieties of limestone are marlmarl
or bog lime,
soil, essentially clay mixed with carbonate of lime, highly valued as a dressing or fertilizer. It crumbles rapidly and easily. Marl in which the lime is in the form of invertebrate shells is called shell marl.
..... Click the link for more information. , chalkchalk,
mineral of calcium carbonate, similar in composition to limestone, but softer. It is characteristically a marine formation and sometimes occurs in great thickness; the chief constituents of these chalk deposits are the shells of minute animals called foraminiferans.
..... Click the link for more information. , ooliteoolite
, rock composed of small concretions, usually of calcium carbonate, containing a nucleus and clearly defined concentric shells. In the British Isles oolitic limestone is characteristic of the middle and upper Jurassic, which was formerly termed the Oolite on this account.
..... Click the link for more information. , travertinetravertine
, form of massive calcium carbonate, CaCO3, resulting from deposition by springs or rivers. It is often beautifully colored and banded as a result of the presence of iron compounds or other (e.g., organic) impurities.
..... Click the link for more information. , dolomitedolomite
. 1 Mineral, calcium magnesium carbonate, CaMg (CO3)2. It is commonly crystalline and is white, gray, brown, or reddish in color with a vitreous to pearly luster. The magnesium is sometimes replaced in part by iron or manganese.
..... Click the link for more information. , and marblemarble,
metamorphic rock composed wholly or in large part of calcite or dolomite crystals, the crystalline texture being the result of metamorphism of limestone by heat and pressure.
..... Click the link for more information. .
a sedimentary rock consisting primarily of calcite CaC03 (more rarely of aragonite). The most frequent impurities in limestone are dolomite, quartz, clay minerals, and the oxides and hydroxides of iron and manganese, as well as pyrite, marcasite, phosphates, gypsum, and organic matter.
The chemical composition of pure limestone approaches the theoretical composition of calcite (56 percent CaCO and 44 percent CaCO2). Limestones in which the content of MgO is between 4 and 17 percent are called dolomitic limestones. As the magnesium content increases, limestones pass through a series of intermediate varieties into the dolomites. Limestones containing between 25 and 50 percent clay particles are called marls. There are also transitional formations between limestones and sandstones. Natural chalk is also a limestone, consisting of 96–99 percent CaCO3. The metamorphism of limestone leads to the formation of marble. Transitional varieties are called marmorate limestones. The nature and degree of granularity in limestones differ; sometimes limestones show well-expressed stratification. Structurally, the rocks are divided into crystalline, organogenic, and fragmented limestones and those with mixed structure. Pure limestones are white or light gray in color. Admixtures of organic substances color limestones black and dark gray, while iron oxides color them yellow, brown, and red.
A distinction is made by origin into organogenic limestones, which are formed through the accumulation of organic remains (coquinas, slag and reef limestone); chemogenic limestones, which occur as a result of calcite precipitating out of solutions;
|Table 1. Characteristics of main lime fertilizers|
(percent of dry substance)
|Characteristics of use|
|CaO . MgO||Impurities|
|Crushed limestone (limestone meal, class A, standard)||to 8||42–56||0–15; clay, sand||Main limestone fertilizer for various crops|
|Crushed limestone (limestone meal, class A, dust)||to 1||42–56||0–15; clay, sand||Same as above, for pneumatic application|
|Crushed dolomite||to 8||39–54||0–15; clay, sand||On strongly podzolized soils, for legpotatoes, flax, and root crops|
|Marl||–||14–42||25–75; clay, sand||For all crops, particularly on light soils|
|Unslaked lime||–||to 100||Slight; clay, sand||Fast-acting fertilizer, particularly for heavy soils|
|Slaked lime (calcium hydroxide)||to 75||Slight; clay, sand||Same as above|
|Tufa||to 50||42–54||5–25; clay, sand 0.5–1 .O P2O5||For all crops (dried in piles before application)|
|Lake lime||to 50||48–56||0–20; clay, sand||Same as above|
|Dolomite meal||to 16||to 52||1.5–4.0; clay, sand||On strongly podzolized soils for legumes, potatoes, flax, and root crops|
|Peat ash||–||8–15||30 SiO2; 1.2 K2O;|
1.1 P2O5; and others
|Comparatively ineffective; used on fields near the areas of peat extraction|
|Shale ash||–||40–45||To 31 SiO2; 1–2 K2O;|
0.5–1.5 P2O5; and others
|For all crops|
|Cement dust||0–2||46–58||15 5 SiO2 and others||Same as above|
|Belite meal||10–15||40–50||30 SiO2; to 2.0 K2O;|
1.2 MnO2; and others
|For all crops|
|By-products from paper and pulp combines||to 40||to 56||Clay||Same as above|
and fragmented limestones, which form through the accumulation of fragments, the products of the destruction of more ancient limestones. Most limestones formed in shallow marine basins by accumulation of organic remains with the simultaneous chemical precipitation of calcite; they formed less often in inland bodies of water. They occur in the form of beds measuring several hundred and sometimes even thousands of meters thick. Limestone beds are encountered among the deposits of all the geological systems, from the Precambrian to the Anthropogenic.
Limestones are used in many sectors of the national economy: as a flux in ferrous metallurgy; for the production of portland cement in the cement industry; for the production of soda, calcium carbide, mineral fertilizers, and other products in the chemical industry; for the purification of sugar beet juice in the sugar production industry; and in the glass industry for giving glass heat resistance, mechanical strength, and resistance to the effect of chemical agents and weathering. In addition, limestone is used in the printing industry and in housing, road, and industrial construction (quarry stone, gravel, stone for laying walls, facing and decorative stone, and so on).
REFERENCESShvetsov, M.S. Petrografiia osadochnykh porod, 3rd ed. Moscow, 1958.
Trebovaniia promyshlennosti k kachestvu mineral ‘nogo syr’ia, 2nd ed., fasc. 10: S.S. Vinogradov, Izvestniaki. Moscow-Leningrad, 1961.
Kurs mestorozhdenii nemetallicheskikh poleznykh iskopaemykh. Moscow, 1969.
G. I. TEODOROVICH