Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, with the chemical formula .[ It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk chalk.][Make your own sidewalk chalk. (1998, July 21). Christian Science Monitor. 13.]
Fine-grained white or lightly tinted forms of gypsum known as alabaster have been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire, and the Nottingham alabasters of Medieval England.
Etymology and history
The word is derived from the Greek language word γύψος (), "plaster".
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.[See:
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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.)
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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, 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.)
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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.
Physical properties
Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C)
The structure of gypsum consists of layers of calcium (Ca2+) and sulfate () ions tightly bound together. These layers are bonded by sheets of anion water molecules via weaker , which gives the crystal perfect cleavage along the sheets (in the {010} plane).
Crystal varieties
Gypsum occurs in nature as flattened and often crystal twinning , and transparent, cleavable masses called selenite. In the form of selenite, gypsum forms some of the largest crystals found in nature, up to long.
Selenite may also occur in a silky, fibrous form, in which case it is commonly called "satin spar".
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.
Occurrence
Gypsum is a common mineral, with thick and extensive evaporite beds in association with . Deposits are known to occur in stratum from as far back as the Archean Aeon.
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 expanse of white gypsum sand, enough to supply the US construction industry with drywall for 1,000 years.
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. This can lead to accumulation of elemental sulfur in oil-bearing formations,
Orbital pictures from the Mars Reconnaissance Orbiter (MRO) have indicated the existence of gypsum dunes in the northern polar region of Mars,[ High-resolution Mars image gallery. University of Arizona] which were later confirmed at ground level by the Mars Exploration Rover (MER) Opportunity.[ NASA Mars Rover Finds Mineral Vein Deposited by Water , NASA, 7 December 2011.]
File:Lechuguilla Chandelier Ballroom.jpg|Large gypsum crystals in Lechuguilla Cave's "chandelier ballroom"
File:Cristales cueva de Naica.JPG|Gypsum crystals in the Cave of the Crystals in Mexico (person at lower right for scale)
File:GypsumCrystalsLakeLucerno.jpg|Gypsum crystals formed as the water evaporated in Lake Lucero, White Sands National Park
File:White Gypsum - geograph.org.uk - 2503198.jpg|Gypsum veins in the silts/marls of the Tea Green and Grey Marls, Blue Anchor, Somerset, United Kingdom
File:Gypsum layers Caprock Canyons 1.JPG|Gypsum veins in Caprock Canyons State Park and Trailway, Texas
File:Yardangs in dunes, White Sands National Park, New Mexico, United States.jpg|Dunes made of small crystals of gypsum, White Sands National Park
Mining
+ Estimated production of Gypsum in 2015
(thousand metric tons) |
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| 1,600 |
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| 700,000 |
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| 39,000 |
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| 290,000 |
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| 450,000 |
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| 450,000 |
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| 55,000 |
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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
Crystals of gypsum up to 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 , and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs and is around 500,000 years old.
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.
Desalination
Gypsum precipitates onto brackish water , a phenomenon known as mineral salt Fouling, such as during brackish water desalination of water with high concentrations of calcium and sulfate. Scaling decreases membrane life and productivity.
A new study has suggested that the formation of gypsum starts as tiny crystals of a mineral called bassanite (2CaSO4·H2O).
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homogeneous nucleation of nanocrystalline bassanite;
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self-assembly of bassanite into aggregates, and
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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.
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.[ To reduce the accumulation and ultimately clear out these stacks, research is underway to find more applications for such waste products.]
Occupational safety
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,
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.
Uses
Gypsum is used in a wide variety of applications:
Construction industry
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Drywall
[* Complimentary list of MasterFormat 2004 Edition numbers and titles (large PDF document)] 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 negligible heat conductivity, giving its plaster some insulative properties.
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are used like concrete blocks in construction.
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Gypsum mortar is an ancient mortar used in construction.
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A component of Portland cement used to prevent flash setting (too rapid hardening) of concrete.
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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.
Agriculture
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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.
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Land reclamation of saline soils, regardless of pH. When gypsum is added to sodic (saline) and acidic soil, the highly soluble form of boron (sodium metaborate) is converted to the less soluble calcium metaborate. The exchangeable sodium percentage is also reduced by gypsum application.
[ Genesis and Management of Sodic (Alkali) Soils. (2017). (n.p.): Scientific Publishers.]
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Other soil conditioner uses: Gypsum reduces aluminium and boron toxicity in acidic soils. It also improves soil structure, water absorption, and aeration.
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Soil water potential monitoring: a gypsum block can be inserted into the soil, and its electrical resistance can be measured to derive soil moisture.
Modeling, sculpture and art
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Plaster for casting moulds and modeling.
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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.
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In the medieval period, and illuminators used it as an ingredient in gesso, which was applied to illuminated letters and gilded with gold in illuminated manuscripts.
Food and drink
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A tofu (soy bean curd) coagulant, making it ultimately a significant source of dietary calcium.
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Adding hard water to water used for brewing.
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Used in baking as a dough conditioner, reducing stickiness, and as a baked goods source of dietary calcium.
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Used in mushroom cultivation to stop grains from clumping together.
Medicine and cosmetics
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Plaster for surgical splints.
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Impression plasters in dentistry.
Other
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An alternative to iron oxide in some thermite mixes.
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Tests have shown that gypsum can be used to remove pollutants such as lead
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from contaminated waters.
Gallery
File:Gypsum-71006.jpg|Green gypsum crystals from Pernatty Lagoon, Mt Gunson, South Australia - its green color is due to presence of copper ions.
File:Gypsum-162462.jpg|Unusual selenite gypsum from the Red River, Winnipeg, Manitoba, Canada
File:Gypsum-47190.jpg|Classic "ram's horn" gypsum from Santa Eulalia, Chihuahua, Mexico, 7.5×4.3×3.8 cm
File:Roses des Sables Tunisie.jpg|Desert rose, 47 cm long
File:Gypsum-53691.jpg|Gypsum from Pernatty Lagoon, Mt Gunson, Stuart Shelf area, Andamooka Ranges - Lake Torrens area, South Australia, Australia
File:Copper-Gypsum-203925.jpg|Gypsum with crystalline native copper inside
File:Gypsum J1.jpg|Gypsum from Swan Hill, Victoria, Australia. The coloring is due to the copper oxide
File:Gypsum-21996.jpg|Waterclear twined crystal of the form known as "Roman sword". Fuentes de Ebro, Zaragoza (Spain)
File:Botryogen-Gypsum-199664.jpg|Bright, cherry-red gypsum crystals 2.5 cm in height colored by rich inclusions of the rare mineral botryogen
File:Gypse Naica.jpg|Gypsum from Naica, Mun. de Saucillo, Chihuahua, Mexico
File:Gypsum-251118.jpg|Golden color gem, "fishtail"-twinned crystals of gypsum sitting atop a "ball" of gypsum which is composed of several single bladed crystals
See also
External links
