Gypsum

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Gypsum
Gips - Lubin, Poland..jpg
General
Category Sulfate minerals
Formula
(repeating unit)
CaSO4·2H2O
Strunz classification 7.CD.40
Crystal system Monoclinic
Crystal class Prismatic (2/m)
H-M symbol: (2/m)
Space group Monoclinic
Space group: I2/a
Unit cell a = 5.679(5), b = 15.202(14)
c = 6.522(6) [Å]; β = 118.43°; Z = 4
Identification
ColorColorless to white; may be yellow, tan, blue, pink, brown, reddish brown or gray due to impurities
Crystal habit Massive, flat. Elongated and generally prismatic crystals
Twinning Very common on {110}
Cleavage Perfect on {010}, distinct on {100}
Fracture Conchoidal on {100}, splintery parallel to [001]
Tenacity Flexible, inelastic
Mohs scale hardness1.5–2 (defining mineral for 2)
Luster Vitreous to silky, pearly, or waxy
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.31–2.33
Optical propertiesBiaxial (+)
Refractive index nα = 1.519–1.521
nβ = 1.522–1.523
nγ = 1.529–1.530
Birefringence δ = 0.010
Pleochroism None
2V angle 58°
Fusibility 5
Solubility Hot, dilute HCl
References [1] [2] [3]
Major varieties
Satin sparPearly, fibrous masses
Selenite Transparent and bladed crystals
Alabaster Fine-grained, slightly colored

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. [3] It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard chalk and wallboard. A massive fine-grained white or lightly tinted variety of gypsum, called alabaster, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire and the Nottingham alabasters of Medieval England. Gypsum also crystallizes as beautiful translucent crystals of selenite (mineral). It also forms as an evaporite mineral and as a hydration product of anhydrite.

Calcium sulfate laboratory and industrial chemical

Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum. It has many uses in industry. All forms are white solids that are poorly soluble in water. Calcium sulfate causes permanent hardness in water.

In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understood.

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.

Contents

The Mohs scale of mineral hardness defines hardness value 2 as gypsum based on scratch hardness comparison.

Mohs scale of mineral hardness qualitative ordinal scale characterizing scratch resistance of various minerals

The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, some of which are more quantitative. The method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. 77 AD. While greatly facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting.

Scratch hardness tests are used to determine the hardness of a material to scratches and abrasion. The earliest test was developed by mineralogist Friedrich Mohs in 1820. It is based on relative scratch hardness, with talc assigned a value of 1 and diamond assigned a value of 10. Mohs' scale had two limitations; it was not linear, and most modern abrasives fall between 9 and 10.

There are a large number of hardness testing methods available. Although it is impossible in many cases to give an exact conversion, it is possible to give an approximate material-specific comparison table e.g. for steels.

Etymology and history

The word gypsum is derived from the Greek word γύψος (gypsos), "plaster". [4] Because the quarries of the Montmartre district of Paris have long furnished burnt gypsum (calcined gypsum) used for various purposes, this dehydrated gypsum became known as plaster of Paris. Upon addition of water, after a few tens of minutes plaster of Paris becomes regular gypsum (dihydrate) again, causing the material to harden or "set" in ways that are useful for casting and construction.

Greek language language spoken in Greece, Cyprus and Southern Albania

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus and other parts of the Eastern Mediterranean and the Black Sea. It has the longest documented history of any living Indo-European language, spanning more than 3000 years of written records. Its writing system has been the Greek alphabet for the major part of its history; other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic, and many other writing systems.

Quarry A place from which a geological material has been excavated from the ground

A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground.

Montmartre hill in the north of Paris, France

Montmartre is a large hill in Paris's 18th arrondissement. It is 130 m (430 ft) high and gives its name to the surrounding district, part of the Right Bank in the northern section of the city. The historic district established by the City of Paris in 1995 is bordered by rue Caulaincourt and rue Custine on the north, rue de Clignancourt on the east, and boulevard de Clichy and boulevard de Rochechouart to the south, containing 60 ha. Montmartre is primarily known for its artistic history, the white-domed Basilica of the Sacré-Cœur on its summit, and as a nightclub district. The other church on the hill, Saint Pierre de Montmartre, built in 1147, was the church of the prestigious Montmartre Abbey. On August 15, 1534, Saint Ignatius of Loyola, Saint Francis Xavier and five other companions bound themselves by vows in the Martyrium of Saint Denis, 11 rue Yvonne Le Tac, the first step in the creation of the Jesuits.

Gypsum was known in Old English as spærstān, "spear stone", referring to its crystalline projections. (Thus, the word spar in mineralogy is by way of comparison to gypsum, referring to any non-ore mineral or crystal that forms in spearlike projections). In the mid-18th century, the German clergyman and agriculturalist Johann Friderich Mayer investigated and publicized gypsum's use as a fertilizer. [5] Gypsum may act as a source of sulfur for plant growth, and in the early 19th century, it was regarded as an almost miraculous fertilizer. American farmers were so anxious to acquire it that a lively smuggling trade with Nova Scotia evolved, resulting in the so-called "Plaster War" of 1820. [6] In the 19th century, it was also known as lime sulfate or sulfate of lime.

Spar (mineralogy) crystalline mineral

Spar is an old mining or mineralogy term used to refer to crystals that have readily discernible faces. A spar will easily break or cleave into rhomboidal, cubical, or laminated fragments with smooth shiny surfaces.

Johann Friedrich Mayer (agriculturist) Agriculturalist

Johann Friedrich Georg Hartmann Mayer was a German Reformed pastor and agricultural reformer, who is considered one of the most important writers on agriculture of his time. He came to prominence through his efforts to promote agricultural reforms, especially with his 1769 publication with new regimes of crop rotation, and his 1773 textbook on rural householders and husbandry.

Physical properties

Gypsum crystals are plastic enough to bend under pressure of the hand. Sample on display at Musee cantonal de geologie de Lausanne. Gypsum deformed cristal-MCG 7747-P4150901-black.jpg
Gypsum crystals are plastic enough to bend under pressure of the hand. Sample on display at Musée cantonal de géologie de Lausanne.

Gypsum is moderately water-soluble (~2.0–2.5 g/l at 25 °C) [7] and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures. When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate, (bassanite, often simply called "plaster") and, if heated further, to anhydrous calcium sulfate (anhydrite). As for anhydrite, its solubility in saline solutions and in brines is also strongly dependent on NaCl (common table salt) concentration. [7]

Anhydrite mineral, anhydrous calcium sulfate

Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

Brine A highly concentrated solution of a salt in water

Brine is a high-concentration solution of salt in water. In different contexts, brine may refer to salt solutions ranging from about 3.5% up to about 26%. Lower levels of concentration are called by different names: fresh water, brackish water, and saline water.

Sodium chloride Chemical compound

Sodium chloride, commonly known as salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/mol respectively, 100 g of NaCl contains 39.34 g Na and 60.66 g Cl. Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. In its edible form of table salt, it is commonly used as a condiment and food preservative. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses. A second major application of sodium chloride is de-icing of roadways in sub-freezing weather.

Gypsum crystals are found to contain anion water and hydrogen bonding. [8]

Hydrogen bond form of association between an electronegative atom and a hydrogen atom attached to a second,relatively electronegative atom;electrostatic interaction,heightened by the small size of hydrogen which permits proximity of the interacting dipoles/charges

A hydrogen bond is a partially electrostatic force of attraction between a hydrogen (H) atom which is bound to a more electronegative atom or group, such as nitrogen (N), oxygen (O), or fluorine (F)—the hydrogen bond donor—and another adjacent atom bearing a lone pair of electrons—the hydrogen bond acceptor. Weak hydrogen bonds occur even with C-H groups as donor

Crystal varieties

Gypsum occurs in nature as flattened and often twinned crystals, and transparent, cleavable masses called selenite. Selenite contains no significant selenium; rather, both substances were named for the ancient Greek word for the Moon.

Selenite may also occur in a silky, fibrous form, in which case it is commonly called "satin spar". Finally, it may also be granular or quite compact. In hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly tinted variety of gypsum, called alabaster, is prized for ornamental work of various sorts. In arid areas, gypsum can occur in a flower-like form, typically opaque, with embedded sand grains called desert rose. It also forms some of the largest crystals found in nature, up to 12 m (39 ft) long, in the form of selenite. [9]

Occurrence

Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as far back as the Archaean eon. [10] Gypsum is deposited from lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near-surface exposures. It is often associated with the minerals halite and sulfur. Gypsum is the most common sulfate mineral. [11] Pure gypsum is white, but other substances found as impurities may give a wide range of colors to local deposits.

Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of the White Sands National Monument in the US state of New Mexico have created a 710 km2 (270 sq mi) expanse of white gypsum sand, enough to supply the construction industry with drywall for 1,000 years. [12] Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when president Herbert Hoover declared the gypsum dunes a protected national monument.

Gypsum is also formed as a by-product of sulfide oxidation, amongst others by pyrite oxidation, when the sulfuric acid generated reacts with calcium carbonate. Its presence indicates oxidizing conditions. Under reducing conditions, the sulfates it contains can be reduced back to sulfide by sulfate-reducing bacteria. Electric power stations burning coal with flue gas desulfurization produce large quantities of gypsum as a byproduct from the scrubbers.

Orbital pictures from the Mars Reconnaissance Orbiter (MRO) have indicated the existence of gypsum dunes in the northern polar region of Mars, [13] which were later confirmed at ground level by the Mars Exploration Rover (MER) Opportunity . [14]

Mining

Estimated production of Gypsum in 2015
(thousand metric tons) [15]
CountryProductionReserves
China 132,000N/A
Iran 22,0001,600
Thailand 12,500N/A
United States 11,500700,000
Turkey 10,000N/A
Spain 6,400N/A
Mexico 5,300N/A
Japan 5,000N/A
Russia 4,500N/A
Italy 4,100N/A
India 3,50039,000
Australia 3,500N/A
Oman 3,500N/A
Brazil 3,300290,000
France 3,300N/A
Canada 2,700450,000
Saudi Arabia 2,400N/A
Algeria 2,200N/A
Germany 1,800450,000
Argentina 1,400N/A
Pakistan 1,300N/A
United Kingdom 1,20055,000
Other countries15,000N/A
World total258,000N/A

Commercial quantities of gypsum are found in the cities of Araripina and Grajaú in Brazil; in Pakistan, Jamaica, Iran (world's second largest producer), Thailand, Spain (the main producer in Europe), Germany, Italy, England, Ireland, Canada [16] and the United States. Large open pit quarries are located in many places including Fort Dodge, Iowa, which sits on one of the largest deposits of gypsum in the world,[ citation needed ] and Plaster City, California, United States, and East Kutai, Kalimantan, Indonesia. Several small mines also exist in places such as Kalannie in Western Australia, where gypsum is sold to private buyers for additions of calcium and sulfur as well as reduction of aluminum toxicities on soil for agricultural purposes.

Crystals of gypsum up to 11 m (36 ft) long have been found in the caves of the Naica Mine of Chihuahua, Mexico. The crystals thrived in the cave's extremely rare and stable natural environment. Temperatures stayed at 58 °C (136 °F), and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tons and is around 500,000 years old. [17]

Synthesis

Synthetic gypsum is recovered via flue-gas desulfurization at some coal-fired power plants. It can be used interchangeably with natural gypsum in some applications.

Gypsum also precipitates onto brackish water membranes, a phenomenon known as mineral salt scaling, such as during brackish water desalination of water with high concentrations of calcium and sulfate. Scaling decreases membrane life and productivity. This is one of the main obstacles in brackish water membrane desalination processes, such as reverse osmosis or nanofiltration. Other forms of scaling, such as calcite scaling, depending on the water source, can also be important considerations in distillation, as well as in heat exchangers, where either the salt solubility or concentration can change rapidly.

A new study has suggested that the formation of gypsum starts as tiny crystals of a mineral called bassanite (CaSO4·0.5H2O). [18] This process occurs via a three-stage pathway:

  1. homogeneous nucleation of nanocrystalline bassanite;
  2. self-assembly of bassanite into aggregates, and
  3. transformation of bassanite into gypsum.

Occupational safety

People can be exposed to gypsum in the workplace by breathing it in, skin contact, and eye contact.

United States

The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for gypsum exposure in the workplace as TWA 15 mg/m3 for total exposure and TWA 5 mg/m3 for respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of TWA 10 mg/m3 for total exposure and TWA 5 mg/m3 for respiratory exposure over an 8-hour workday. [19]

Uses

Gypsum works, Valencian Museum of Ethnology. 2.-Calera. Cal i guix (26561676342).jpg
Gypsum works, Valencian Museum of Ethnology.

Gypsum is used in a wide variety of applications:

See also

Related Research Articles

Alabaster Lightly colored, translucent, and soft calcium minerals, typically gypsum

Alabaster is a mineral or rock that is soft, often used for carving, and is processed for plaster powder. Archaeologists and the stone processing industry use the word differently from geologists. The former use is in a wider sense that includes varieties of two different minerals: the fine-grained massive type of gypsum and the fine-grained banded type of calcite. Geologists define alabaster only as the gypsum type. Chemically, gypsum is a hydrous sulfate of calcium, while calcite is a carbonate of calcium.

Calcite carbonate mineral

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".

Celestine (mineral) sulfate mineral

Celestine or celestite is a mineral consisting of strontium sulfate (SrSO4). The mineral is named for its occasional delicate blue color. Celestine and the carbonate mineral strontianite are the principal sources of the element strontium, commonly used in fireworks and in various metal alloys.

Weathering Breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earths atmosphere, biota and waters

Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms. Weathering occurs in situ, that is, in the same place, with little or no movement, and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations.

Plaster general term for a broad range of building materials

Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English "plaster" usually means a material used for the interiors of buildings, while "render" commonly refers to external applications. Another imprecise term used for the material is stucco, which is also often used for plasterwork that is worked in some way to produce relief decoration, rather than flat surfaces.

Calcium hydroxide chemical compound

Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is obtained when calcium oxide (called lime or quicklime) is mixed, or slaked with water. It has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater is the common name for a saturated solution of calcium hydroxide.

Sinus Meridiani albedo feature on Mars

Sinus Meridiani is an albedo feature on Mars stretching east-west just south of that planet's equator. It was named by the French astronomer Camille Flammarion in the late 1870s.

Selenite (mineral) mineral variety

Selenite, also known as satin spar, desert rose, or gypsum flower are four crystal structure varieties of the mineral gypsum. These four varieties of gypsum may be grouped together and called selenite.

Potassium sulfate chemical compound

Potassium sulfate (in British English potassium sulphate (SOP), also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is the inorganic compound with formula K2SO4. It is a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and a source of sulfur.

Ammonium sulfate chemical compound

Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen and 24% sulfur.

Lime (material) calcium-containing inorganic mineral

Lime is a calcium-containing inorganic mineral composed primarily of oxides, and hydroxide, usually calcium oxide and/ or calcium hydroxide. It is also the name for calcium oxide which occurs as a product of coal seam fires and in altered limestone xenoliths in volcanic ejecta. The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.

Naica Mine mine

The Naica Mine of the Mexican state of Chihuahua, is a working mine that contains extremely large selenite crystals. Located in Naica in the municipality of Saucillo, the Naica Mine is a lead, zinc and silver mine operated by Industrias Peñoles, Mexico's largest lead producer. Caverns discovered during mining operations contain crystals of selenite (gypsum) as large as 1.2 m (4 ft) in diameter and 15 m (50 ft) long. Peñoles announced in October 2015 that it was indefinitely suspending operations at Naica Mine.

Gypcrete or gypcrust is a hardened layer of soil, consisting of around 95% gypsum. Gypcrust is an arid zone duricrust. It can also occur in a semiarid climate in a basin with internal drainage, and is initially developed in a playa as an evaporate. Gypcrete is the arid climate's equivalent to calcrete, which is a duricrust that is unable to generate in very arid climates.

Glauberite sulfate mineral

Glauberite is a monoclinic sodium calcium sulfate mineral with the formula Na2Ca(SO4)2.

This page provides supplementary chemical data on calcium sulfate.

Cement mill

A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement. Most cement is currently ground in ball mills and also vertical roller mills which are more effective than ball mills.

Cave of the Crystals cave

Cave of the Crystals or Giant Crystal Cave is a cave connected to the Naica Mine at a depth of 300 metres (980 ft), in Naica, Chihuahua, Mexico.

Bassanite sulfate mineral

Bassanite is a calcium sulfate mineral with formula CaSO4·0.5(H2O) or 2CaSO4·H2O. In other words it has half a water per CaSO4 unit hence its synonym hemihydrate.

References

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