a = 5.679(5), b = 15.202(14) c = 6.522(6) Å; β = 118.43°; Z = 4
Identification
Color
Colorless (in transmitted light) to white; often tinged other hues due to impurities; may be yellow, tan, blue, pink, dark brown, reddish brown or gray
The word gypsum is derived from the
Greek word γύψος (gypsos), "plaster".[9] 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 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 is moderately water-soluble (~2.0–2.5 g/L at 25 °C)[13] 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 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]
Gypsum occurs in nature as flattened and often
twinnedcrystals, 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
evaporite beds in association with
sedimentary rocks. Deposits are known to occur in
strata from as far back as the
Archaeaneon.[16] Gypsum is deposited from lake and sea water, as well as in
hot springs, from
volcanic vapors, and sulfate solutions in
veins.
Hydrothermalanhydrite 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
sulfideoxidation, amongst others by
pyriteoxidation, 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. This can lead to accumulation of elemental sulfur in oil-bearing formations,[19] such as salt domes,[20] where it can be mined using the
Frasch process[21] Electric power stations burning coal with
flue gas desulfurization produce large quantities of gypsum as a byproduct from the scrubbers.
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[25] 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,[26] 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 tonnes (61 short tons) and is around 500,000 years old.[27]
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
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.[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 (CaSO4·0.5H2O).[30] This process occurs via a three-stage pathway:
homogeneous nucleation of nanocrystalline bassanite;
self-assembly of bassanite into aggregates, and
transformation of bassanite into gypsum.
Refinery waste
The production of
phosphate fertilizers requires breaking down calcium-containing
phosphate rock with acid, producing calcium sulfate waste known as
phosphogypsum (PG). This form of gypsum is contaminated by impurities found in the rock, namely
fluoride,
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]
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]
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 AgeCrete, gypsum was employed in building construction at locations where wood was previously used.[38]
Agriculture
Fertilizer: In the late 18th and early 19th centuries, Nova Scotia gypsum, often referred to as plaster, was a highly sought fertilizer for wheat fields in the United States.[39] Gypsum provides two of the
secondary plant macronutrients, calcium and sulfur. Unlike limestone, it generally does not affect soil pH.[40]
Other
soil conditioner uses: Gypsum reduces aluminium and boron toxicity in acidic soils. It also improves soil structure, improving water absorption and aeration.[40]
Soil
water potential monitoring: a gypsum block can be inserted into soil, its electrical resistance measured to derive soil moisture.[44]
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]
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.
^Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2003).
"Gypsum"(PDF). Handbook of Mineralogy. Vol. V (Borates, Carbonates, Sulfates). Chantilly, VA, US: Mineralogical Society of America.
ISBN978-0962209703.
Archived(PDF) from the original on 6 February 2006.
Thaer, Albrecht Daniel; Shaw, William, trans.; Johnson, Cuthbert W., trans. (1844).
The Principles of Agriculture. Vol. 1. London, England: Ridgway. pp. 519–520.{{
cite book}}: CS1 maint: multiple names: authors list (
link)
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.)
^Smith, Joshua (2007). Borderland smuggling: Patriots, loyalists, and illicit trade in the Northeast, 1780–1820. Gainesville, FL: UPF. pp. passim.
ISBN978-0-8130-2986-3.
^Mandal, Pradip K; Mandal, Tanuj K (2002). "Anion water in gypsum (CaSO4·2H2O) and hemihydrate (CaSO4·1/2H2O)". Cement and Concrete Research. 32 (2): 313.
doi:
10.1016/S0008-8846(01)00675-5.
^Sassen, Roger; Chinn, E.W.; McCabe, C. (December 1988). "Recent hydrocarbon alteration, sulfate reduction and formation of elemental sulfur and metal sulfides in salt dome cap rock". Chemical Geology. 74 (1–2): 57–66.
Bibcode:
1988ChGeo..74...57S.
doi:
10.1016/0009-2541(88)90146-5.
^Graham, Gerald S. (1938). "The Gypsum Trade of the Maritime Provinces: Its Relation to American Diplomacy and Agriculture in the Early Nineteenth Century". Agricultural History. 12 (3): 209–223.
JSTOR3739630.
^Ley, Willy (October 1961).
"The Home-Made Land". For Your Information. Galaxy Science Fiction. pp. 92–106.
^Durner, W.; Or, D. (2006).
"Soil water potential measurement"(PDF). In Anderson, M.G. (ed.). Encyclopedia of hydrological sciences. John Wiley & Sons Ltd.
ISBN978-0471491033.
Archived(PDF) from the original on 16 June 2022. Retrieved 23 May 2022.
^Austin, R.T. (March 1983). "Treatment of broken legs before and after the introduction of gypsum". Injury. 14 (5): 389–394.
doi:
10.1016/0020-1383(83)90089-X.
PMID6347885.
^Drennon, David G.; Johnson, Glen H. (February 1990). "The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts". The Journal of Prosthetic Dentistry. 63 (2): 233–241.
doi:
10.1016/0022-3913(90)90111-O.
PMID2106026.
^Govender, Desania R.; Focke, Walter W.; Tichapondwa, Shepherd M.; Cloete, William E. (20 June 2018). "Burn Rate of Calcium Sulfate Dihydrate–Aluminum Thermites". ACS Applied Materials & Interfaces. 10 (24): 20679–20687.
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^Rodriguez, J. D.; Jimenez, A.; Prieto, M.; Torre, L.; Garcia-Granda, S. (2008). "Interaction of gypsum with As(V)-bearing aqueous solutions: Surface precipitation of guerinite, sainfeldite, and Ca2NaH(AsO4)2⋅6H2O, a synthetic arsenate". American Mineralogist. 93 (5–6): 928.
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^Rodríguez-Blanco, Juan Diego; Jiménez, Amalia; Prieto, Manuel (2007). "Oriented Overgrowth of Pharmacolite (CaHAsO4⋅2H2O) on Gypsum (CaSO4⋅2H2O)". Cryst. Growth Des. 7 (12): 2756–2763.
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