Limestone

Limestone
Sedimentary rock
Torcaldeantequera.jpg
Limestone outcrop in the Torcal de Antequera nature reserve of Málaga, Spain
Composition
Calcium carbonate: inorganic crystalline calcite or organic calcareous material

Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

About 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock.

Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.

Description

Limestone quarry at Cedar Creek, Virginia, USA
Cutting limestone blocks at a quarry in Gozo, Malta
Limestone as building material
La Zaplaz formations in the Piatra Craiului Mountains, Romania.

Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. These organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts.

Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules, diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrial detritus) carried in by rivers.

Some limestones do not consist of grains, and are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular (oolite) appearance.

The primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters (see lysocline). Limestones may also form in lacustrine[1] and evaporite depositional environments.[2][3]

Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases.

Impurities (such as clay, sand, organic remains, iron oxide, and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces.

Limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures.

Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells.

During regional metamorphism that occurs during the mountain building process (orogeny), limestone recrystallizes into marble.

Limestone is a parent material of Mollisol soil group.

Other Languages
Alemannisch: Kalk
العربية: حجر جيري
aragonés: Calsinera
asturianu: Caliza
azərbaycanca: Əhəng daşı
বাংলা: চুনাপাথর
Bân-lâm-gú: Chio̍h-hoe-giâm
башҡортса: Эзбизташ
беларуская: Вапняк
беларуская (тарашкевіца)‎: Вапняк
български: Варовик
Boarisch: Koichstoa
bosanski: Krečnjak
čeština: Vápenec
Cymraeg: Calchfaen
dansk: Kalksten
Deutsch: Kalkstein
eesti: Lubjakivi
Ελληνικά: Ασβεστόλιθος
español: Caliza
Esperanto: Kalkoŝtono
estremeñu: Cal
euskara: Kareharri
فارسی: سنگ آهک
français: Calcaire
Frysk: Kalkstien
Gaeilge: Aolchloch
galego: Calcaria
한국어: 석회암
հայերեն: Կրաքար
हिन्दी: चूना पत्थर
hrvatski: Vapnenac
Bahasa Indonesia: Gamping
íslenska: Kalksteinn
italiano: Calcare
עברית: אבן גיר
ქართული: კირქვა
қазақша: Әктас
Kiswahili: Chokaa mawe
Кыргызча: Акиташ теги
latviešu: Kaļķakmens
lietuvių: Klintis
Limburgs: Kalkstein
македонски: Варовник
Bahasa Melayu: Batu kapur
မြန်မာဘာသာ: ထုံးကျောက်
Nederlands: Kalksteen
नेपाली: चुनढुङ्गा
नेपाल भाषा: सख्वाःल्वहं
日本語: 石灰岩
norsk: Kalkstein
norsk nynorsk: Kalkstein
occitan: Calcari
پنجابی: لائم پتھر
polski: Wapień
português: Calcário
română: Calcar
Runa Simi: Isku rumi
русский: Известняк
Scots: Limestane
සිංහල: හුණු ගල්
Simple English: Limestone
slovenčina: Vápenec
slovenščina: Apnenec
Soomaaliga: Nuurad
српски / srpski: Кречњак
srpskohrvatski / српскохрватски: Vapnenac
suomi: Kalkkikivi
svenska: Kalksten
татарча/tatarça: Известьташ
тоҷикӣ: Оҳаксанг
Türkçe: Kireç taşı
українська: Вапняк
Tiếng Việt: Đá vôi
吴语: 石灰岩
ייִדיש: קאלכשטיין
粵語: 石灰岩
中文: 石灰岩