Gypsum

Source: Wikipedia, the free encyclopedia.
This article is about the mineral. For other uses, see Gypsum (disambiguation).

Gypsum
2V angle
58°
Fusibility5
SolubilityHot, dilute HCl
References[2][3][4]
Major varieties
Satin sparPearly, fibrous masses
SeleniteTransparent and bladed crystals
AlabasterFine-grained, slightly colored

Gypsum is a soft

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

Fine-grained white or lightly tinted forms of gypsum known as

Medieval England
.

Etymology and history

The word

plaster of Paris. Upon adding water, after a few dozen 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.[10]

Gypsum was known in Old English as spærstān, "spear stone", referring to its crystalline projections. Thus, the word spar in mineralogy, by comparison to gypsum, refers 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.[11] 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.[12]

Physical properties

Gypsum crystals are soft 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)

calcium sulfate hemihydrate (bassanite, often simply called "plaster") and, if heated further, to anhydrous calcium sulfate (anhydrite). As with anhydrite, the solubility of gypsum in saline solutions and in brines is also strongly dependent on NaCl (common table salt) concentration.[13]

The structure of gypsum consists of layers of calcium (Ca2+) and sulfate (SO2−4) ions tightly bound together. These layers are bonded by sheets of

anion water molecules via weaker hydrogen bonding, which gives the crystal perfect cleavage along the sheets (in the {010} plane).[4][14]

Crystal varieties

Main article: Selenite (mineral)

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.[15]

Occurrence

Gypsum is a common mineral, with thick and extensive

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.[17]
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 Park in the US state of New Mexico have created a 710 km2 (270 sq mi) expanse of white gypsum sand, enough to supply the US construction industry with drywall for 1,000 years.[18] 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

flue gas desulfurization
produce large quantities of gypsum as a byproduct from the scrubbers.

Orbital pictures from the

Opportunity.[23]

Mining

Estimated production of Gypsum in 2015
(thousand metric tons)[24]
Country Production Reserves
China 132,000 —
Iran 22,000 1,600
Thailand 12,500 —
United States 11,500 700,000
Turkey 10,000 —
Spain 6,400 —
Mexico 5,300 —
Japan 5,000 —
Russia 4,500 —
Italy 4,100 —
India 3,500 39,000
Australia 3,500 —
Oman 3,500 —
Brazil 3,300 290,000
France 3,300 —
Canada 2,700 450,000
Saudi Arabia 2,400 —
Algeria 2,200 —
Germany 1,800 450,000
Argentina 1,400 —
Pakistan 1,300 —
United Kingdom 1,200 55,000
Other countries 15,000 —
World total 258,000 —

Commercial quantities of gypsum are found in the cities of

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 tonnes (61 short tons) and is around 500,000 years old.[27]

Synthesis

Synthetic gypsum is produced as a waste product or by-product in a range of industrial processes.

Desulfurization

Flue gas desulfurization gypsum (FGDG) is recovered at some coal-fired power plants. The main contaminants are Mg, K, Cl, F, B, Al, Fe, Si, and Se. They come both from the limestone used in desulfurization and from the coal burned. This product is pure enough to replace natural gypsum in a wide variety of fields including drywalls, water treatment, and cement set retarder. Improvements in flue gas desulfurization have greatly reduced the amount of toxic elements present.[28]

Desalination

Gypsum precipitates onto brackish water

brackish water desalination of water with high concentrations of calcium and sulfate. Scaling decreases membrane life and productivity.[29] 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 (2CaSO4·H2O).[30] 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.

Refinery waste

The production of

silica, radioactive elements such as radium, and heavy metal elements such as cadmium.[31] Similarly, production of titanium dioxide produces titanium gypsum (TG) due to neutralization of excess acid with lime. The product is contaminated with silica, fluorides, organic matters, and alkalis.[32]

Impurities in refinery gypsum waste have, in many cases, prevented them from being used as normal gypsum in fields such as construction. As a result, waste gypsum is stored in stacks indefinitely, with significant risk of leaching their contaminants into water and soil.[31] To reduce the accumulation and ultimately clear out these stacks, research is underway to find more applications for such waste products.[32]

Occupational safety

NFPA 704
fire diamond
[33]
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
0
0
Gypsum

People can be exposed to gypsum in the workplace by breathing it in, skin contact, and eye contact. Calcium sulfate per se is nontoxic and is even approved as a food additive,[34] but as powdered gypsum, it can irritate skin and mucous membranes.[35]

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 eight-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 eight-hour workday.[35]

Uses

Gypsum works, Valencian Museum of Ethnology
Old Alfarb kiln for making plaster as a construction material
Map of gypsum deposits in northern Ohio, black squares indicate the location of deposits, from "Geography of Ohio", 1923

Gypsum is used in a wide variety of applications:

Construction industry

  • Gypsum board[36] is primarily used as a finish for walls and ceilings, and is known in construction as plasterboard, "sheetrock", or drywall. Gypsum provides a degree of fire-resistance to these materials and glass fibers are added to their composition to accentuate this effect. Gypsum has little heat conductivity, giving its plaster some insulative properties.[37]
  • Gypsum blocks are used like concrete blocks in building construction.
  • Gypsum mortar
    is an ancient mortar used in building construction.
  • A component of Portland cement used to prevent flash setting (too rapid hardening) of concrete.
  • A wood substitute in the ancient world: For example, when wood became scarce due to deforestation on Bronze Age Crete, gypsum was employed in building construction at locations where wood was previously used.[38]

Agriculture

Modeling, sculpture and art

  • Plaster for casting moulds and modeling.
  • As alabaster, a material for sculpture, it was used especially in the ancient world before steel was developed, when its relative softness made it much easier to carve.[45] During the Middle Ages and Renaissance, it was preferred even to marble.[46]
  • In the medieval period, scribes and illuminators used it as an ingredient in gesso, which was applied to illuminated letters and gilded with gold in illuminated manuscripts.[47]

Food and drink

  • A tofu (soy bean curd) coagulant, making it ultimately a significant source of dietary calcium.[48]
  • Adding hardness to water used for brewing.[49]
  • Used in baking as a dough conditioner, reducing stickiness, and as a baked-goods source of dietary calcium.[50] The primary component of mineral yeast food.[51]
  • Used in mushroom cultivation to stop grains from clumping together.

Medicine and cosmetics

Other

  • An alternative to iron oxide in some thermite mixes.[54]
  • Tests have shown that gypsum can be used to remove pollutants such as lead[55] or arsenic[56][57] from contaminated waters.

Gallery

  • Unusual gypsum specimens from around the world
  • Green gypsum crystals from Pernatty Lagoon, Mt Gunson, South Australia - its green color is due to presence of copper ions.
    Green gypsum crystals from Pernatty Lagoon, Mt Gunson, South Australia - its green color is due to presence of copper ions.
  • Unusual selenite gypsum from the Red River, Winnipeg, Manitoba, Canada
    Unusual selenite gypsum from the Red River, Winnipeg, Manitoba, Canada
  • Classic "ram's horn" gypsum from Santa Eulalia, Chihuahua, Mexico, 7.5×4.3×3.8 cm
    Classic "ram's horn" gypsum from Santa Eulalia, Chihuahua, Mexico, 7.5×4.3×3.8 cm
  • Desert rose, 47 cm long
    Desert rose, 47 cm long
  • Gypsum from Pernatty Lagoon, Mt Gunson, Stuart Shelf area, Andamooka Ranges - Lake Torrens area, South Australia, Australia
    Gypsum from Pernatty Lagoon, Mt Gunson, Stuart Shelf area, Andamooka Ranges - Lake Torrens area, South Australia, Australia
  • Gypsum with crystalline native copper inside
    Gypsum with crystalline native copper inside
  • Gypsum from Swan Hill, Victoria, Australia. The coloring is due to the copper oxide
    Gypsum from Swan Hill, Victoria, Australia. The coloring is due to the copper oxide
  • Waterclear twined crystal of the form known as "Roman sword". Fuentes de Ebro, Zaragoza (Spain)
    Waterclear twined crystal of the form known as "Roman sword". Fuentes de Ebro, Zaragoza (Spain)
  • Bright, cherry-red gypsum crystals 2.5 cm in height colored by rich inclusions of the rare mineral botryogen
    Bright, cherry-red gypsum crystals 2.5 cm in height colored by rich inclusions of the rare mineral botryogen
  • Gypsum from Naica, Mun. de Saucillo, Chihuahua, Mexico
    Gypsum from Naica, Mun. de Saucillo, Chihuahua, Mexico
  • Golden color gem, "fishtail"-twinned crystals of gypsum sitting atop a "ball" of gypsum which is composed of several single bladed crystals
    Golden color gem, "fishtail"-twinned crystals of gypsum sitting atop a "ball" of gypsum which is composed of several single bladed crystals

See also

References

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  5. ^ Institute, Canadian Conservation (14 September 2017). "Care of Objects Made of Plaster of Paris – Canadian Conservation Institute (CCI) Notes 12/2". www.canada.ca. Retrieved 20 January 2023.
  6. ^ Make your own sidewalk chalk. (1998, July 21). Christian Science Monitor. 13.
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  8. ^ "Definition of DRYWALL". www.merriam-webster.com. Retrieved 20 January 2023.
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    • Klaus Herrmann (1990), "Mayer, Johann Friedrich", Neue Deutsche Biographie (in German), vol. 16, Berlin: Duncker & Humblot, pp. 544–545; (full text online) From p. 544: " … er bewirtschaftete nebenbei ein Pfarrgüttchen, … für die Düngung der Felder mit dem in den nahen Waldenburger Bergen gefundenen Gips einsetzte." ( … he also managed a small parson's estate, on which he repeatedly conducted agricultural experiments. In 1768, he first published the fruits of his experiences during this time as "Instruction about Gypsum", in which he espoused the fertilizing of fields with the gypsum that was found in the nearby Waldenburg mountains.)
    • Beckmann, Johann (1775). Grundsätze der deutschen Landwirthschaft [Fundamentals of German Agriculture] (in German) (2nd ed.). Göttingen, (Germany): Johann Christian Dieterich. p. 60. From p. 60: "Schon seit undenklichen Zeiten … ein Gewinn zu erhalten seyn wird." (Since times immemorial, in our vicinity, in the ministry of Niedeck [a village southeast of Göttingen], one has already made this use of gypsum; but Mr. Mayer has the merit to have made it generally known. In the History of Farming in Kupferzell, he had depicted a crushing mill (p. 74), in order to pulverize gypsum, from which a profit has been obtained, albeit with difficulty.)
    • Mayer, Johann Friderich (1768). Lehre vom Gyps als vorzueglich guten Dung zu allen Erd-Gewaechsen auf Aeckern und Wiesen, Hopfen- und Weinbergen [Instruction in gypsum as an ideal good manure for all things grown in soil on fields and pastures, hops yards and vineyards] (in German). Anspach, (Germany): Jacob Christoph Posch.
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External links

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