Everything about Limestone totally explained
Limestone is a
sedimentary rock composed largely of the
mineral calcite (
calcium carbonate: CaCO
3).
Description
Limestone often contains variable amounts of
silica in the form of
chert or
flint, as well as varying amounts of
clay,
silt and
sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly
marine organisms. These organisms secrete shells that settle out of the water column and are deposited on
ocean floors as
pelagic ooze or alternatively is conglomerated in a coral reef (see
lysocline for information on calcite dissolution). Secondary calcite may also 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 that of
oolites (oolitic limestone) which can be recognized by its granular appearance.
Limestone makes up about 10% of the total volume of all sedimentary rocks. Limestones may also form in both
lacustrine and
evaporite depositional environments.
Calcite can be either
dissolved by groundwater 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.
When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures.
Karst topography and
caves develop in carbonate rocks due to their
solubility in dilute
acidic
groundwater. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation.
Coastal limestones are often eroded by organisms which bore into the rock by various means. This process is known as
bioerosion. It is most common in the tropics, and it's known throughout the
fossil record (see Taylor and Wilson, 2003).
Because of impurities, such as
clay, sand, organic remains,
iron oxide and other materials, many limestones exhibit different colors, especially on
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.
Folk and
Dunham classifications are used to describe limestones more precisely.
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 that's supersaturated with 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.
Limestone landscape
Limestone is partially soluble, especially in
acid, and therefore forms many
erosional
landforms. These include
limestone pavements,
pot holes,
cenotes,
caves and
gorges. Such erosion landscapes are known as karsts. Limestone is less
resistant than most
igneous rocks, but more resistant than most other
sedimentary rocks. Limestone is therefore usually associated with hills and
downland and occurs in regions with other sedimentary rocks, typically
clays.
Bands of limestone emerge from the
Earth's surface in often spectacular rocky outcrops and
islands. Examples include the
Burren in Co. Clare, Ireland; the
Verdon Gorge in
France;
Malham Cove in
North Yorkshire and the
Isle of Wight,
England; on
Fårö near the Swedish island of
Gotland, the
Niagara Escarpment in
Canada/
USA, Notch Peak in
Utah, and the
Ha Long Bay National Park in
Vietnam.
Unique habitats are found on
alvars, extremely level expanses of limestone with thin soil mantles. The largest such expanse in
Europe is the
Stora Alvaret on the island of
Oland,
Sweden. Another area with large quantities of limestone is the island of
Gotland, Sweden. Huge quarries in northwestern Europe, such as those of Mount Saint Peter (Belgium/Netherlands), extend for more than a hundred kilometers.
The world's largest limestone quarry is at
Michigan Limestone and Chemical Company in
Rogers City, Michigan.
Uses of limestone
Limestone is very common in
architecture, especially in
North America and
Europe. Many landmarks across the world, including the pyramids in
Egypt, are made of limestone. So many buildings in
Kingston, Ontario, Canada were constructed from it that it's nicknamed the 'Limestone City'. On the island of
Malta, a variety of limestone called Globigerina limestone was for a long time the only building material available, and is still very frequently used on all types of buildings and sculptures. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving. It is also long-lasting and stands up well to exposure. However, it's a very heavy material, making it impractical for tall buildings, and relatively expensive as a building material.
Limestone was most popular in the early 20th and late 19th centuries.
Train stations,
banks and other structures from that era are normally made of limestone. Limestone is used as a facade on some
skyscrapers, but only in thin plates for covering rather than solid blocks. In the United States,
Indiana, most notably the Bloomington area, has long been a source of high quality quarried limestone, called
Indiana limestone. Many famous buildings in
London are built from
Portland limestone.
Limestone was also a very popular building block in the Middle Ages in the areas where it occurred since it's hard, durable, and commonly occurs in easily accessible surface exposures. Many medieval churches and castles in Europe are made of limestone.
Beer stone was a popular kind of limestone for medieval buildings in southern England.
Limestone and marble are very reactive to acid solutions, making
acid rain a significant problem. Many limestone statues and building surfaces have suffered severe damage due to acid rain. Acid-based cleaning chemicals can also etch limestone, which should only be cleaned with a neutral or mild alkaline-based cleaner.
Other uses include:
- The manufacture of quicklime (calcium oxide) and slaked lime (calcium hydroxide);
- Cement and mortar;
- Pulverized limestone is used as a soil conditioner to neutralize acidic soil conditions;
- Crushed for use as aggregate—the solid base for many roads;
- Geological formations of limestone are among the best petroleum reservoirs;
- As a reagent in desulfurizations;
- Glass making, in some circumstances;
- Toothpaste;
- Suppression of methane explosions in underground coal mines
- Added to bread as a source of calcium
Further Information
Get more info on 'Limestone'.
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