Gypsum
Template:Short description Template:About Template:Use American English Template:Use dmy dates Template:Infobox mineral Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula Template:Chem2.<ref name=Cornelis/> 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.<ref>Template:Cite web</ref><ref>Make your own sidewalk chalk. (1998, July 21). Christian Science Monitor. 13.</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref> Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite. The 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 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
[edit]The word gypsum is derived from the Greek word Template:Lang (Template:Transliteration), "plaster".<ref>Template:Cite web</ref> 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.<ref name=Szostakowski>Template:Cite journal</ref>
Gypsum was known in Old English as Template:Lang, "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.<ref>See:
- Template:Cite book
- Template:NDB 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.)
- Template:Cite book 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.)
- Template:Cite book</ref> 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.<ref>Template:Cite book</ref>
Physical properties
[edit]
Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C)<ref name="Bock_1961">Template:Cite journal</ref> 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 sodium chloride (common table salt) concentration.<ref name="Bock_1961"/>
The structure of gypsum consists of layers of calcium (Ca2+) and sulfate (Template:Chem2) 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).<ref name=Cornelis/><ref>Template:Cite journal</ref>
Crystal varieties
[edit]Template:Main 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 Template:Convert long, in the form of selenite.<ref>Template:Cite journal</ref>
Occurrence
[edit]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.<ref name="Cockell">Template:Cite journal</ref> 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.<ref name="DHZ1966">Template:Cite book</ref> 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 Template:Convert expanse of white gypsum sand, enough to supply the US construction industry with drywall for 1,000 years.<ref name='The Albuquerque Journal 1999-02-07'>Template:Cite news</ref> 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. This can lead to accumulation of elemental sulfur in oil-bearing formations,<ref>Template:Cite journal</ref> such as salt domes,<ref>Template:Cite journal</ref> where it can be mined using the Frasch process<ref name =Ullmann>Template:Ullmann</ref> 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,<ref>High-resolution Mars image gallery. University of Arizona</ref> which were later confirmed at ground level by the Mars Exploration Rover (MER) Opportunity.<ref>NASA Mars Rover Finds Mineral Vein Deposited by Water Template:Webarchive, NASA, 7 December 2011.</ref>
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Large gypsum crystals in Lechuguilla Cave's "chandelier ballroom"
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Gypsum crystals in the Cave of the Crystals in Mexico (person at lower right for scale)
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Gypsum crystals formed as the water evaporated in Lake Lucero, White Sands National Park
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Gypsum veins in the silts/marls of the Tea Green and Grey Marls, Blue Anchor, Somerset, United Kingdom
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Gypsum veins in Caprock Canyons State Park and Trailway, Texas
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Dunes made of small crystals of gypsum, White Sands National Park
Mining
[edit]| Country | Production | Reserves |
|---|---|---|
| China | 132,000 | Template:N/A |
| Iran | 22,000 | 1,600 |
| Thailand | 12,500 | Template:N/A |
| United States | 11,500 | 700,000 |
| Turkey | 10,000 | Template:N/A |
| Spain | 6,400 | Template:N/A |
| Mexico | 5,300 | Template:N/A |
| Japan | 5,000 | Template:N/A |
| Russia | 4,500 | Template:N/A |
| Italy | 4,100 | Template:N/A |
| India | 3,500 | 39,000 |
| Australia | 3,500 | Template:N/A |
| Oman | 3,500 | Template:N/A |
| Brazil | 3,300 | 290,000 |
| France | 3,300 | Template:N/A |
| Canada | 2,700 | 450,000 |
| Saudi Arabia | 2,400 | Template:N/A |
| Algeria | 2,200 | Template:N/A |
| Germany | 1,800 | 450,000 |
| Argentina | 1,400 | Template:N/A |
| Pakistan | 1,300 | Template:N/A |
| United Kingdom | 1,200 | 55,000 |
| Other countries | 15,000 | Template:N/A |
| World total | 258,000 | Template:N/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<ref name='Mining Canada'>Template:Cite web</ref> 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,<ref>Template:Cite book</ref> 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 aluminium toxicities on soil for agricultural purposes.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>
Crystals of gypsum up to Template:Convert 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 Template:Cvt, and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs Template:Convert and is around 500,000 years old.<ref>Template:Cite news</ref>
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Golden gypsum crystals from Winnipeg
Synthesis
[edit]Synthetic gypsum is produced as a waste product or by-product in a range of industrial processes.
Desulfurization
[edit]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.<ref name="pmid31561139">Template:Cite journal</ref>
Desalination
[edit]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.<ref>Template:Cite journal</ref> 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).<ref>Template:Cite journal</ref> 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
[edit]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.<ref name=Taylor>Template:Cite journal</ref> 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.<ref name="pmid26495867">Template:Cite journal</ref>
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.<ref name=Taylor/> To reduce the accumulation and ultimately clear out these stacks, research is underway to find more applications for such waste products.<ref name="pmid26495867"/>
Occupational safety
[edit]Template:NFPA 704 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,<ref name=pc>Template:Cite web</ref> but as powdered gypsum, it can irritate skin and mucous membranes.<ref name="cdc">Template:Cite web</ref>
United States
[edit]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.<ref name="cdc"/>
Uses
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Gypsum is used in a wide variety of applications:
Construction industry
[edit]- Gypsum board<ref>*Complimentary list of MasterFormat 2004 Edition numbers and titles (large PDF document)</ref> 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.<ref name="Bonewitz-2008">Template:Cite book</ref>
- Gypsum blocks are used like concrete blocks in construction.
- Gypsum mortar is an ancient mortar used in 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.<ref>Template:Cite journal</ref>
Agriculture
[edit]- 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.<ref>Template:Cite journal</ref> Gypsum provides two of the secondary plant macronutrients, calcium and sulfur. Unlike limestone, it generally does not affect soil pH.<ref name="soilsorg"/>
- 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.<ref>Genesis and Management of Sodic (Alkali) Soils. (2017). (n.p.): Scientific Publishers.</ref><ref>Template:Cite journal</ref> The Zuiderzee Works uses gypsum for the recovered land.<ref name="ley196110">Template:Cite magazine</ref>
- Other soil conditioner uses: Gypsum reduces aluminium and boron toxicity in acidic soils. It also improves soil structure, water absorption, and aeration.<ref name="soilsorg">Template:Cite web</ref>
- Soil water potential monitoring: a gypsum block can be inserted into the soil, and its electrical resistance can be measured to derive soil moisture.<ref>Template:Cite encyclopedia</ref>
Modeling, sculpture and art
[edit]- 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.<ref>Template:Cite book</ref> During the Middle Ages and Renaissance, it was preferred even to marble.<ref>Template:Cite journal</ref>
- 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.<ref>Template:Cite book</ref>
Food and drink
[edit]- A tofu (soy bean curd) coagulant, making it ultimately a significant source of dietary calcium.<ref>Template:Cite book</ref>
- Adding hardness to water used for brewing.<ref>Template:Cite web</ref>
- Used in baking as a dough conditioner, reducing stickiness, and as a baked goods source of dietary calcium.<ref>Template:Cite web</ref> The primary component of mineral yeast food.<ref>Template:Cite web</ref>
- Used in mushroom cultivation to stop grains from clumping together.
Medicine and cosmetics
[edit]- Plaster for surgical splints.<ref>Template:Cite journal</ref>
- Impression plasters in dentistry.<ref>Template:Cite journal</ref>
Other
[edit]- An alternative to iron oxide in some thermite mixes.<ref>Template:Cite journal</ref>
- Tests have shown that gypsum can be used to remove pollutants such as lead<ref>Template:Cite journal</ref> or arsenic<ref>Template:Cite journal</ref><ref>Template:Cite journal
</ref> from contaminated waters.
Gallery
[edit]- Unusual gypsum specimens from around the world
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Green gypsum crystals from Pernatty Lagoon, Mt Gunson, South Australia - its green color is due to presence of copper ions.
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Unusual selenite gypsum from the Red River, Winnipeg, Manitoba, Canada
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Classic "ram's horn" gypsum from Santa Eulalia, Chihuahua, Mexico, 7.5×4.3×3.8 cm
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Desert rose, 47 cm long
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Gypsum from Pernatty Lagoon, Mt Gunson, Stuart Shelf area, Andamooka Ranges - Lake Torrens area, South Australia, Australia
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Gypsum with crystalline native copper inside
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Gypsum from Swan Hill, Victoria, Australia. The coloring is due to the copper oxide
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Waterclear twined crystal of the form known as "Roman sword". Fuentes de Ebro, Zaragoza (Spain)
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Bright, cherry-red gypsum crystals 2.5 cm in height colored by rich inclusions of the rare mineral botryogen
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Gypsum from Naica, Mun. de Saucillo, Chihuahua, Mexico
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Golden color gem, "fishtail"-twinned crystals of gypsum sitting atop a "ball" of gypsum which is composed of several single bladed crystals
