Portlandite is a

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. ...

-bearing mineral typically included in the

oxide mineral The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the ...

class. It is the naturally occurring form of

calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has ma ...

(Ca(OH)₂) and the calcium analogue of

brucite Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg( OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists ...

(Mg(OH)₂).

Occurrence

Portlandite occurs in a variety of environments. At the type location in Northern Ireland it occurs as an alteration of

calc–silicate rock A calc–silicate rock is a rock produced by metasomatic alteration of existing rocks in which calcium silicate minerals such as diopside and wollastonite are produced. Calc–silicate skarn or hornfels occur within impure limestone or dolomite st ...

s by

contact metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...

of larnite–

spurrite Spurrite is a white, yellow or light blue mineral with monoclinic crystals. Its chemical formula is Ca5( Si O4)2 CO3. Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks.Smith, J.V. (19 ...

. It occurs as

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

deposits in the

Vesuvius Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma-stratovolcano located on the Gulf of Naples in Campania, Italy, about east of Naples and a short distance from the shore. It is one of ...

area. In Jebel Awq,

Oman Oman ( ; ar, عُمَان ' ), officially the Sultanate of Oman ( ar, سلْطنةُ عُمان ), is an Arabian country located in southwestern Asia. It is situated on the southeastern coast of the Arabian Peninsula, and spans the mouth of ...

it occurs as precipitates from an

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

emanating from

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

bedrock. In the

Chelyabinsk Chelyabinsk ( rus, Челя́бинск, p=tɕɪˈlʲæbʲɪnsk, a=Ru-Chelyabinsk.ogg; ba, Силәбе, ''Siläbe'') is the administrative center and largest city of Chelyabinsk Oblast, Russia. It is the seventh-largest city in Russia, with a ...

coal basin of

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

it is produced by combustion of

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

seams and similarly by spontaneous combustion of

bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...

in the Hatrurim Formation of the

Negev desert The Negev or Negeb (; he, הַנֶּגֶב, hanNegév; ar, ٱلنَّقَب, an-Naqab) is a desert and semidesert region of southern Israel. The region's largest city and administrative capital is Beersheba (pop. ), in the north. At its southe ...

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

and the Maqarin area,

Jordan Jordan ( ar, الأردن; tr. ' ), officially the Hashemite Kingdom of Jordan,; tr. ' is a country in Western Asia. It is situated at the crossroads of Asia, Africa, and Europe, within the Levant region, on the East Bank of the Jordan Rive ...

. It also occurs in the

manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...

mining area of Kuruman,

Cape Province The Province of the Cape of Good Hope ( af, Provinsie Kaap die Goeie Hoop), commonly referred to as the Cape Province ( af, Kaapprovinsie) and colloquially as The Cape ( af, Die Kaap), was a province in the Union of South Africa and subsequen ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...

in the

Kalahari Desert The Kalahari Desert is a large semi-arid sandy savanna in Southern Africa extending for , covering much of Botswana, and parts of Namibia and South Africa. It is not to be confused with the Angolan, Namibian, and South African Namib coastal d ...

where it occurs as large crystals and masses. It occurs in association with

afwillite Afwillite is a calcium hydroxide nesosilicate mineral with formula Ca3(SiO3OH)2·2H2O. It occurs as glassy, colorless to white prismatic monoclinic crystals. Its Mohs scale hardness is between 3 and 4. It occurs as an alteration mineral in cont ...

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

, larnite,

halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

brownmillerite Brownmillerite is a rare oxide mineral with chemical formula . It is named for Lorrin Thomas Brownmiller (1902–1990), chief chemist of the Alpha Portland Cement Company, Easton, Pennsylvania. Discovery and occurrence The chemical compound ...

, hydrocalumite, mayenite and

ettringite Ettringite is a hydrous calcium aluminium sulfate mineral with formula: . It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of ...

. It was first described in 1933 for an occurrence at

Scawt Hill Scawt Hill is a volcanic plug in County Antrim, Northern Ireland, in the borough of Larne, 5 km from the village of Ballygally. It gets its name from the Ulster Scots "" meaning scaly, scabby or rugged. Alternatively, '' 'scawt' '' mea ...

Larne Larne (, , the name of a Gaelic territory) is a town on the east coast of County Antrim, Northern Ireland, with a population of 18,755 at the 2011 Census. It is a major passenger and freight roll-on roll-off port. Larne is administered by Mid a ...

County Antrim County Antrim (named after the town of Antrim, ) is one of six counties of Northern Ireland and one of the thirty-two counties of Ireland. Adjoined to the north-east shore of Lough Neagh, the county covers an area of and has a population ...

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label=Ulster Scots dialect, Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is #Descriptions, variously described as ...

. It was named portlandite because the chemical calcium hydroxide is a common hydrolysis product of

Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19t ...

References

{{Reflist Calcium minerals Hydroxide minerals Trigonal minerals Minerals in space group 164