Caliche (Mineral) - AbsoluteAstronomy.com

Caliche is a sedimentary rock, a hardened deposit of calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

. This calcium carbonate cements together other materials, including gravel, sand, clay, and silt. It is found in aridisol and mollisol soil orders. Caliche occurs worldwide, generally in arid

Arid

A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...

or semiarid regions, including in central and western Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, in the Kalahari Desert

Kalahari Desert

The Kalahari Desert is a large semi-arid sandy savannah in Southern Africa extending , covering much of Botswana and parts of Namibia and South Africa, as semi-desert, with huge tracts of excellent grazing after good rains. The Kalahari supports more animals and plants than a true desert...

, in the High Plains

High Plains (United States)

The High Plains are a subregion of the Great Plains mostly in the Western United States, but also partly in the Midwest states of Nebraska, Kansas, and South Dakota, generally encompassing the western part of the Great Plains before the region reaches the Rocky Mountains...

of the western USA

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, and in the Sonoran Desert

Sonoran Desert

The Sonoran Desert is a North American desert which straddles part of the United States-Mexico border and covers large parts of the U.S. states of Arizona and California and the northwest Mexican states of Sonora, Baja California, and Baja California Sur. It is one of the largest and hottest...

. Caliche is also known as hardpan
Hardpan
In soil science, agriculture and gardening, hardpan or ouklip is a general term for a dense layer of soil, usually found below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water...

, calcrete, kankar (in India), or duricrust
Duricrust
Duricrust is a hard layer on or near the surface of soil. Duricrusts can range in thickness from a few millimeters or centimeters to several meters....

. The term caliche is Spanish and is originally from the Latin calx, meaning lime

Lime (mineral)

Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...

.

Caliche is generally light colored but can range from white to light pink to reddish-brown, depending on the impurities present. It is generally found on or near the surface, but it can be found in deeper subsoil deposits as well. The layers can vary from a few inches to feet thick, and multiple layers can exist in a single location.

In northern Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

and Peru

Peru

Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

, caliche also refers to mineral deposits that include nitrate

Nitrate

The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...

salts. Caliche can also refer to various claylike deposits in Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

and Colombia

Colombia

Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...

. In addition, it has been used to describe some forms of quartzite

Quartzite

Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...

, bauxite

Bauxite

Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...

, kaolinite

Kaolinite

Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...

, laterite

Laterite

Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...

, chalcedony

Chalcedony

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic...

, opal

Opal

Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...

, and soda niter.

A similar material, composed of calcium sulfate

Calcium sulfate

Calcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...

rather than calcium carbonate

Calcium carbonate

, is called gypcrust
Gypcrust
Gypcrete or gypcrust is a hardened layer of soil, consisting of around 95% gypsum . It forms in a manner similar to that of caliche, which is composed of calcium carbonate....

.

How it forms

Caliche generally forms when minerals are leached

Leaching (pedology)

In pedology, leaching is the loss of mineral and organic solutes due to percolation. It is a mechanism of soil formation. It is distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and elluviated materials tend to be lost from topsoil and...

from the upper layer of the soil (the A horizon) and accumulate in the next layer (the B horizon), at depths of approximately 3 to 10 feet under the surface. Caliche generally consists of carbonates in semiarid regions, while in arid regions, less soluble minerals will form caliche layers after all the carbonates have been leached from the soil. The calcium carbonate that is deposited accumulates, first forming grains, then small clumps, then a discernible layer, and finally a thicker, solid bed. As the caliche layer forms, the layer gradually becomes deeper, eventually moving into the parent material

Parent material

In soil science, parent material is the underlying geological material in which soil horizons form...

, which lies under the upper soil horizons.

However, caliche can also form in other ways. It can form when water rises through capillary action

Capillary action

Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...

. In an arid region, rainwater will sink into the ground very quickly. Later, as the surface dries out, the water below the surface will rise, carrying dissolved minerals from lower layers upward with it. This water movement forms a caliche that tends to grow thinner and branch out as it nears the surface. Plants can contribute to the formation of caliche as well. The plant roots take up water through transpiration

Transpiration

Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants , especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants...

, leaving behind the dissolved calcium carbonate, which precipitates to form caliche. Caliche can also form on outcrops of porous rocks or in rock fissures where water is trapped and evaporates. In general, caliche deposition is a slow process, but if enough moisture is present in an otherwise arid site, it can accumulate fast enough to block a drain pipe.

Examples of natural occurrence

While the formation of other caliches is relatively well understood, the origin of Chilean caliche is not clearly known. One possibility is that the deposits were formed when a prehistoric inland sea evaporated. Another theory is that it was deposited due to weathering of the Andes

Andes

The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

.

One of the world's largest deposits of calcrete is in the Makgadikgadi Pans in Botswana

Botswana

Botswana, officially the Republic of Botswana , is a landlocked country located in Southern Africa. The citizens are referred to as "Batswana" . Formerly the British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966...

, where surface calcretes occur at the location of a now desiccated prehistoric lake.

Building applications

Caliche (the calcium carbonate mineral) is used in construction worldwide. The caliche reserves in the Llano Estacado

Llano Estacado

Llano Estacado , commonly known as the Staked Plains, is a region in the Southwestern United States that encompasses parts of eastern New Mexico and northwestern Texas, including the South Plains and parts of the Texas Panhandle...

in Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

can be used in the manufacture of Portland cement

Portland cement

Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

; the caliche meets the chemical composition requirements and has been used as a principal raw material in Portland cement production in at least one Texas plant. Where the calcium carbonate content is over 80 %, caliche can also be fired and used as a source of lime

Lime (mineral)

in areas, which can then be used for soil stabilization.
When mixed with small amounts of either pozzolan or Portland cement, caliche can also be used as a building material that will exceed the building code

Building code

A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the...

requirements for unfired masonry

Masonry

Masonry is the building of structures from individual units laid in and bound together by mortar; the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, stone, marble, granite, travertine, limestone; concrete block, glass block, stucco, and...

materials. For example, caliche was used to build some of the Mayan

Maya civilization

The Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period The Maya is a Mesoamerican...

buildings in the Yucatán Peninsula

Yucatán Peninsula

The Yucatán Peninsula, in southeastern Mexico, separates the Caribbean Sea from the Gulf of Mexico, with the northern coastline on the Yucatán Channel...

in Mexico

Mexico

. A dormitory in Ingram, Texas

Ingram, Texas

Ingram is a city in Kerr County, Texas, United States. The population was 1,740 at the 2000 census.-Geography:Ingram is located at , on the Guadalupe River in the Texas Hill Country...

and a demonstration building in Carrizo Springs, Texas

Carrizo Springs, Texas

Carrizo Springs is a city in and the county seat of Dimmit County, Texas, United States. The population was 5,655 at the 2000 census.The name of the town comes from the local springs, which were named by the Spanish for the cane grass that once grew around them. It is the oldest town in Dimmit...

for the United States Department of Energy

United States Department of Energy

The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

were also built using caliche as part of studies by the Center for Maximum Potential Building Systems

Center for Maximum Potential Building Systems

The Center for Maximum Potential Building Systems , established in 1975, is a non-profit education, research, and demonstration organization specializing in life cycle planning and design...

.

In many areas, caliche is also used for road construction, either as a surfacing material or, more commonly, as a base material. It is one of the most common road materials used in Southern Africa

Southern Africa

Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...

. Caliche is widely used as a base material when it is locally available and cheap. However it does not hold up to moisture, (rain), and is never used if a hard rock base material such as limestone is available.

Sugar refining

A nearly pure source of calcium carbonate is necessary to refine sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

. It must contain at least 95 % calcium carbonate (CaCO₃) and have a low magnesium content. In addition, the material must meet certain physical requirements so it does not break down when burned. Although caliche does not generally meet all of the requirements for sugar refining, it is used in areas where another source of calcium carbonate, such as limestone, is not present. While the use of caliche necessitates beneficiation

Beneficiation

In mining, beneficiation is a variety of processes whereby extracted ore from mining is separated into mineral and gangue, the former suitable for further processing or direct use....

to meet the requirements, its use can still be significantly cheaper than shipping in the needed limestone.

Chilean Caliche

In the Atacama Desert

Atacama Desert

The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...

in northern Chile

Chile

, there are vast deposits of a mixture, also referred to as caliche, composed of gypsum

Gypsum

Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

, sodium chloride

Sodium chloride

Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

, and other salts and sand, associated to salitre
Nitratine
Nitratine or nitratite, also known as cubic niter , soda niter or Chile saltpeter , is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Nitratine crystallizes in the trigonal system, but rarely occurs as well formed crystals. It is isostructural with calcite...

("Chile saltpeter"). Salitre, in turn, is a composite of sodium nitrate

Sodium nitrate

Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...

(NaNO₃) and potassium nitrate

Potassium nitrate

Potassium nitrate is a chemical compound with the formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre , from medieval Latin sal petræ: "stone salt" or possibly "Salt...

(KNO₃). Salitre was an important source of export revenue for Chile until World War I, when in Europe both nitrates began to be industrially produced in large quantities.

These deposits are the largest known natural source of nitrates in the world, containing up to 25% sodium nitrate and 3% potassium nitrate, as well as iodate minerals, sodium chloride, sodium sulfate

Sodium sulfate

Sodium sulfate is the sodium salt of sulfuric acid. When anhydrous, it is a white crystalline solid of formula Na2SO4 known as the mineral thenardite; the decahydrate Na2SO4·10H2O has been known as Glauber's salt or, historically, sal mirabilis since the 17th century. Another solid is the...

, and sodium borate (borax). The caliche beds are from 0.2 to 5 meters thick, and they are mined and refined to produce a variety of products, including sodium nitrate (for agriculture or industry uses), potassium nitrate, sodium sulfate, iodine

Iodine

Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

, and iodine derivatives.

Problems caused by Caliche

Caliche beds can cause many problems when trying to grow plants. First, an impermeable caliche layer prevents water from draining properly, which can keep the roots from getting enough oxygen. Salts can also build up in the soil due to the lack of drainage. Both of these situations are detrimental to plant growth. Second, the impermeable nature of caliche beds also prevents plant roots from going through the bed, which means the roots have a limited supply of nutrients, water, and space, so they cannot develop normally. Third, caliche beds can also cause the surrounding soil to be basic (have a high pH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

). The basic soil, along with calcium carbonate from the caliche, can prevent plants from getting enough nutrients, especially iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

. An iron deficiency

Iron deficiency (plant disorder)

Iron deficiency is a plant disorder also known as "lime-induced chlorosis". It can be confused with manganese deficiency. A deficiency in the soil is rare but iron can be unavailable for absorption if soil pH is not between about 5 and 6.5. A common problem is when the soil is too alkaline...

will cause the plant’s youngest leaves to become yellow. Soil saturation

Water content

Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...

above the caliche bed can make the condition worse.

External links

Conquering Home Yard Caliche

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