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56-396: Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate , with the chemical formula CaSO 4 ·2H 2 O . 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 . Gypsum also crystallizes as translucent crystals of selenite . It forms as an evaporite mineral and as

112-556: 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 . The word gypsum

168-512: A recommended exposure limit (REL) of TWA 10 mg/m for total exposure and TWA 5 mg/m for respiratory exposure over an eight-hour workday. Gypsum is used in a wide variety of applications: Sulfate mineral The sulfate minerals are a class of minerals that include the sulfate ion ( SO 4 ) within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments , as gangue minerals in hydrothermal veins and as secondary minerals in

224-409: A compact, banded travertine stone or a stalagmitic limestone colored with swirling bands of cream and brown. In general, ancient alabaster is calcite in the wider Middle East , including Egypt and Mesopotamia , while it is gypsum in medieval Europe . Modern alabaster is most likely calcite but may be either. Both are easy to work and slightly soluble in water. They have been used for making

280-479: A delicate green variety at La Pedrara , in the district of Tecali , near Puebla . Onyx-marble occurs also in the district of Tehuacán and at several localities in the US including California , Arizona , Utah , Colorado and Virginia . Gypsum alabaster is softer than calcite alabaster. It was used primarily in medieval Europe, and is also used in modern times. "Mosul marble" is a kind of gypsum alabaster found in

336-474: A range of industrial processes. 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

392-411: 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. 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

448-403: A smooth, polished surface is washed with dishwashing liquid , it will become rough, dull and whiter, losing most of its translucency and lustre. The finer kinds of alabaster are employed largely as an ornamental stone , especially for ecclesiastical decoration and for the rails of staircases and halls. Alabaster is mined and then sold in blocks to alabaster workshops. There they are cut to

504-476: 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. Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C) and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures. When gypsum

560-508: A variety of indoor artwork and carving, as they will not survive long outdoors. The two types are readily distinguished by their different hardness: gypsum alabaster ( Mohs hardness 1.5 to 2) is so soft that a fingernail scratches it, while calcite (Mohs hardness 3) cannot be scratched in this way but yields to a knife. Moreover, calcite alabaster, being a carbonate, effervesces when treated with hydrochloric acid , while gypsum alabaster remains almost unaffected. The English word "alabaster"

616-493: 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 km (270 sq mi) expanse of white gypsum sand, enough to supply the US construction industry with drywall for 1,000 years. Commercial exploitation of

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672-500: Is a hydrous sulfate of calcium , whereas calcite is a carbonate of calcium. As types of alabaster, gypsum and calcite have similar properties, such as light color, translucence, and soft stones that can be carved and sculpted ; thus the historical use and application of alabaster for the production of carved, decorative artefacts and objets d’art . Calcite alabaster also is known as: onyx-marble , Egyptian alabaster , and Oriental alabaster , which terms usually describe either

728-497: Is a porous stone and can be "dyed" into any colour or shade, a technique used for centuries. For this the stone needs to be fully immersed in various pigmentary solutions and heated to a specific temperature. The technique can be used to disguise alabaster. In this way a very misleading imitation of coral that is called "alabaster coral" is produced. Typically only one type is sculpted in any particular cultural environment, but sometimes both have been worked to make similar pieces in

784-585: Is also found, in smaller quantity, at Watchet in Somerset , near Penarth in Glamorganshire , and elsewhere. In Cumbria it occurs largely in the New Red rocks, but at a lower geological horizon. The alabaster of Nottinghamshire and Derbyshire is found in thick nodular beds or "floors" in spheroidal masses known as "balls" or "bowls" and in smaller lenticular masses termed "cakes". At Chellaston, where

840-508: Is contaminated by impurities found in the rock, namely fluoride , silica , radioactive elements such as radium , and heavy metal elements such as cadmium . 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. Impurities in refinery gypsum waste have, in many cases, prevented them from being used as normal gypsum in fields such as construction. As

896-586: Is derived from the Greek word γύψος ( gypsos ), "plaster". 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. Gypsum

952-543: Is derived: onyx-marble or alabaster-onyx, or sometimes simply (and wrongly) as onyx . Egyptian alabaster has been worked extensively near Suez and Assiut . This stone variety is the "alabaster" of the ancient Egyptians and Bible and is often termed Oriental alabaster , since the early examples came from the Far East . The Greek name alabastrites is said to be derived from the town of Alabastron in Egypt , where

1008-444: Is even approved as a food additive, but as powdered gypsum, it can irritate skin and mucous membranes. 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/m for total exposure and TWA 5 mg/m for respiratory exposure over an eight-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set

1064-591: 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. The structure of gypsum consists of layers of calcium (Ca) and sulfate ( SO 2− 4 ) ions tightly bound together. These layers are bonded by sheets of anion water molecules via weaker hydrogen bonding , which gives

1120-545: Is on display in Sir John Soane's Museum , London ; it is carved in a single block of translucent calcite alabaster from Alabastron. Algerian onyx-marble has been quarried largely in the province of Oran . Calcite alabaster was quarried in ancient Israel in the cave known as the Twins Cave near Beit Shemesh . Herod used this alabaster for baths in his palaces. In Mexico , there are famous deposits of

1176-461: 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. 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

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1232-516: Is sent to Florence for figure-sculpture, while the common kinds are carved locally, into vases, lights, and various ornamental objects. These items are objects of extensive trade, especially in Florence, Pisa , and Livorno . In the 3rd century BC the Etruscans used the alabaster of Tuscany from the area of modern-day Volterra to produce funeral urns , possibly taught by Greek artists. During

1288-752: Is the Fuentes- Azaila area, in the Tertiary Ebro Basin. The other is the Calatayud -Teruel Basin, which divides the Iberian Range in two main sectors (NW and SE). The abundance of Aragonese alabaster was crucial for its use in architecture, sculpture and decoration. There is no record of use by pre-Roman cultures, so the first ones to use alabaster from Aragon may have been the Romans, who produced vessels from alabaster following

1344-589: The Aljafería Palace, together with other interesting elements like capitals, reliefs and inscriptions, were made using alabaster, but it was during the artistic and economic blossoming of the Renaissance that Aragonese alabaster reached its golden age. In the 16th century sculptors in Aragon chose alabaster for their best works. They were adept at exploiting its lighting qualities and generally speaking

1400-496: The Archaean eon . 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. Pure gypsum is white, but other substances found as impurities may give

1456-528: The British Museum , are some of the best known. Gypsum alabaster was widely used for small sculpture for indoor use in the ancient world, especially in ancient Egypt and Mesopotamia . Fine detail could be obtained in a material with an attractive finish without iron or steel tools. Alabaster was used for vessels dedicated for use in the cult of the deity Bast in the culture of the ancient Egyptians, and thousands of gypsum alabaster artifacts dating to

1512-632: The Cathedral of Our Lady of the Angels , dedicated in 2002 by the Los Angeles, California, Archdiocese . The cathedral incorporates special cooling to prevent the panes from overheating and turning opaque. The ancients used the calcite type, while the modern Los Angeles cathedral employs gypsum alabaster. There are also multiple examples of alabaster windows in ordinary village churches and monasteries in northern Spain. Calcite alabaster, harder than

1568-583: The Ebro Valley in Aragon , Spain , which has the world's largest known exploitable deposits. According to a brochure published by the Aragon government, alabaster has elsewhere either been depleted, or its extraction is so difficult that it has almost been abandoned or is carried out at a very high cost. There are two separate sites in Aragon, both are located in Tertiary basins. The most important site

1624-677: The English Reformation the making of altarpiece sets was discontinued, but funerary monument work in reliefs and statues continued. In addition to the carvings still in Britain (particularly the Nottingham Castle Museum , British Museum , and Victoria and Albert Museum ), trade in mineral alabaster (other than the antiques trade) is ongoing as far afield as the Musée de Cluny , Spain, and Scandinavia. Alabaster

1680-554: The Middle Ages the craft of alabaster was almost completely forgotten. A revival started in the mid-16th century, and until the beginning of the 17th century alabaster work was strictly artistic and did not expand to form a large industry. In the 17th and 18th centuries production of artistic, high-quality Renaissance-style artifacts stopped altogether, replaced by less sophisticated, cheaper items better suited for large-scale production and commerce. The new industry prospered, but

1736-505: The oxidizing zone of sulfide mineral deposits. The chromate and manganate minerals have a similar structure and are often included with the sulfates in mineral classification systems. Sulfate minerals include: IMA -CNMNC proposes a new hierarchical scheme (Mills et al., 2009). This list uses it to modify the Classification of Nickel–Strunz ( mindat.org , 10 ed, pending publication). Alabaster Chemically, gypsum

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1792-501: The 14th and 15th centuries the carving into small statues and sets of relief panels for altarpieces was a valuable local industry in Nottingham , as well as a major English export. These were usually painted, or partly painted. It was also used for the effigies, often life size, on tomb monuments , as the typical recumbent position suited the material's lack of strength, and it was cheaper and easier to work than good marble. After

1848-695: The Elder and Ptolemy wrote that the stone used for ointment jars called alabastra came from a region of Egypt known as Alabastron or Alabastrites. The purest alabaster is a snow-white material of fine uniform grain, but it often is associated with an oxide of iron , which produces brown clouding and veining in the stone. The coarser varieties of gypsum alabaster are converted by calcination into plaster of Paris , and are sometimes known as "plaster stone". The softness of alabaster enables it to be carved readily into elaborate forms, but its solubility in water renders it unsuitable for outdoor work. If alabaster with

1904-726: The Greek and Egyptian models. It seems that since the reconstruction of the Roman Wall in Zaragoza in the 3rd century AD with alabaster, the use of this material became common in building for centuries. Muslim Saraqusta (Zaragoza) was also called "Medina Albaida", the White City, due to the appearance of its alabaster walls and palaces, which stood out among gardens, groves and orchards by the Ebro and Huerva Rivers. The oldest remains in

1960-699: 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, 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

2016-493: The amount of toxic elements present. 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. 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

2072-418: 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,

2128-488: 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. Synthetic gypsum is produced as a waste product or by-product in

2184-670: The crystal perfect cleavage along the sheets (in the {010} plane). 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 ,

2240-829: The evolution of alabaster use after World War II are Volterran Umberto Borgna , the "first alabaster designer", and later on the architect and industrial designer Angelo Mangiarotti . Gypsum alabaster is a common mineral, which occurs in England in the Keuper marls of the Midlands , especially at Chellaston in Derbyshire , at Fauld in Staffordshire , and near Newark in Nottinghamshire . Deposits at all of these localities have been worked extensively. In

2296-652: The existence of gypsum dunes in the northern polar region of Mars, which were later confirmed at ground level by the Mars Exploration Rover (MER) Opportunity . 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 and

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2352-496: The finished art pieces retained their natural color. In modern Europe , the centre of the alabaster trade is Florence, Italy . Tuscan alabaster occurs in nodular masses embedded in limestone, interstratified with marls of Miocene and Pliocene age. The mineral is worked largely by means of underground galleries, in the district of Volterra . Several varieties are recognized—veined, spotted, clouded, agatiform, and others. The finest kind, obtained principally from Castellina ,

2408-450: The gypsum variety, was used in ancient Egypt and the wider Middle East (except Assyrian palace reliefs ), and also in modern times. It is found as either a stalagmitic deposit from the floor and walls of limestone caverns , or as a kind of travertine , similarly deposited in springs of calcareous water. Its deposition in successive layers gives rise to the banded appearance that the marble often shows on cross-section, from which its name

2464-564: The late 4th millennium BC also have been found in Tell Brak (modern Nagar ), in Syria . In Mesopotamia, gypsum alabaster was the material of choice for figures of deities and devotees in temples, as in a figure believed to represent the deity Abu dating to the first half of the 3rd millennium BC, which is kept in New York. Much of the world's alabaster is extracted from the centre of

2520-463: The local alabaster is known as "Patrick", it has been worked into ornaments under the name of "Derbyshire spar"―a term more properly applied to fluorspar . Black alabaster is a rare anhydrite form of the gypsum-based mineral. The black form is found in only three veins in the world, one each in United States , Italy , and China . Alabaster Caverns State Park , near Freedom, Oklahoma ,

2576-422: The needed size ("squaring"), and then are processed in different techniques: turned on a lathe for round shapes, carved into three-dimensional sculptures , chiselled to produce low relief figures or decoration; and then given an elaborate finish that reveals its transparency, colour, and texture. In order to diminish the translucency of the alabaster and to produce an opacity suggestive of true marble,

2632-593: The newly developed craft, artistic work became again possible, chiefly by Volterran sculptor Albino Funaioli . After a short slump, the industry was revived again by the sale of mass-produced mannerist Expressionist sculptures. It was further enhanced in the 1920s by a new branch that created ceiling and wall lamps in the Art Deco style, culminating in participation at the 1925 International Exposition of Modern Industrial and Decorative Arts in Paris . Important names in

2688-480: The north of modern Iraq , which was used for the Assyrian palace reliefs of the 9th to 7th centuries BC; these are the largest type of alabaster sculptures to have been regularly made. The relief is very low and the carving detailed, but large rooms were lined with continuous compositions on slabs around 7 feet (2.1 m) high. The Lion Hunt of Ashurbanipal and military Lachish reliefs , both 7th century and in

2744-499: The reduced need for skilled craftsmen left few of them still working. The 19th century brought a boom to the industry, largely due to the "traveling artisans" who offered their wares to the palaces of Europe, as well as to America and the East. In the 19th century new processing technology was also introduced, allowing for the production of custom-made, unique pieces, as well as the combination of alabaster with other materials. Apart from

2800-691: The same place and time. This was the case with small flasks of the alabastron type made in Cyprus from the Bronze Age into the Classical period. When cut into thin sheets, alabaster is translucent enough to be used for small windows. It was used for this purpose in Byzantine churches and later in medieval ones, especially in Italy . Large sheets of Aragonese gypsum alabaster are used extensively in

2856-422: The statues are immersed in a bath of water and heated gradually—nearly to the boiling point—an operation requiring great care, because if the temperature is not regulated carefully, the stone acquires a dead-white, chalky appearance. The effect of heating appears to be a partial dehydration of the gypsum. If properly treated, it very closely resembles true marble and is known as " marmo di Castellina ". Alabaster

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2912-482: The stone was quarried. The locality may owe its name to the mineral; though the origin of the mineral name is obscure The "Oriental" alabaster was highly esteemed for making small perfume bottles or ointment vases called alabastra ; the vessel name has been suggested as a possible source of the mineral name. In Egypt, craftsmen used alabaster for canopic jars and various other sacred and sepulchral objects. The sarcophagus of Seti I , found in his tomb near Thebes ,

2968-583: 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, such as salt domes, where it can be mined using the Frasch process 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

3024-560: 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 (2CaSO 4 ·H 2 O). This process occurs via a three-stage pathway: 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

3080-567: Was borrowed from Old French alabastre , in turn derived from Latin alabaster , and that from Greek ἀλάβαστρος ( alábastros ) or ἀλάβαστος ( alábastos ). The Greek words denoted a vase of alabaster. The name may be derived further from ancient Egyptian a-labaste , which refers to vessels of the Egyptian goddess Bast . She was represented as a lioness and frequently depicted as such in figures placed atop these alabaster vessels. Ancient Roman authors Pliny

3136-523: 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. Gypsum may act as

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