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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