limestone

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 oxide), as a building stone, and for ornamentation. Among the important varieties of limestone are marl, chalk, oolite, travertine, dolomite, and marble.

limestone

Rock of sedimentary origin composed principally of calcite, dolomite, or both; used as a building stone or crushed-stone aggregate, or burnt to produce lime. See also: Stone

Limestone

 

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
	Moisture (percent)	Content (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).

REFERENCES

Shvetsov, 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

limestone

[′līm‚stōn]

(petrology)

A sedimentary rock composed dominantly (more than 95) of calcium carbonate, principally in the form of calcite; examples include chalk and travertine.

Any rock containing 80% or more of calcium carbonate or magnesium carbonate.

limestone

Rock of sedimentary origin composed principally of calcite or dolomite or both; used as building stone or crushed-stone aggregate or burnt to produce lime.

limestone

a sedimentary rock consisting mainly of calcium carbonate, deposited as the calcareous remains of marine animals or chemically precipitated from the sea: used as a building stone and in the manufacture of cement, lime, etc.