Ettringite

Ettringite

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Ettringite is a hydrous calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 sulfate mineral
Sulfate mineral
The sulfate minerals are a class of minerals which include the sulfate ion within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal veins and as secondary minerals in the oxidizing zone of sulfide mineral deposits...

 with formula: Ca6Al2(SO4)3(OH)12·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system
Crystal system
In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...

. The prismatic crystals are typically colorless, turning white on partial dehydration.

Discovery and occurrence



Ettringite was first described in 1874 for an occurrence near the Ettringer Bellerberg volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

, Ettringen
Ettringen, Mayen-Koblenz
Ettringen is a municipality in the district of Mayen-Koblenz in Rhineland-Palatinate, western Germany....

, Rheinland-Pfalz, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. It occurs within metamorphically altered limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 adjacent to igneous intrusive rocks or within xenolith
Xenolith
A xenolith is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption...

s. It also occurs as weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...

 crusts on larnite
Larnite
Larnite is a mineral, known as dicalcisum silicate.Dicalcium silicate is chemically, β–Ca2SiO4, sometimes represented by the formula 2CaO·SiO2.When used in the cement industry, the mineral is usually referred to as Belite....

 in the Hatrurim Formation
Hatrurim Formation
The Hatrurim Formation or mottled zone is a geologic formation in the Negev Desert in Israel and in western Jordan. It includes late Cretaceous to Eocene aged impure limestone along with coal bearing chalk and marl. The rocks have been subjected to pyrometamorphism resulting from combustion of...

 of Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

. It occurs associated with portlandite
Portlandite
Portlandite is a rare oxide mineral, the naturally occurring form of calcium hydroxide . It is the calcium analogue of brucite .-Occurrence:...

, afwillite
Afwillite
Afwillite is a calcium hydroxide nesosilicate mineral with formula Ca32.2H2O. It occurs as glassy, colorless to white prismatic monoclinic crystals. Its Mohs scale hardness is between 3 and 4...

 and hydrocalumite at Scawt Hill, Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 and with afwillite, hydrocalumite, mayenite
Mayenite
Mayenite , Ca12Al14O33, is a rare cubic mineral of cubic symmetry, originally reported from Eifel volcanic complex . It is also found at pyrometamorphic sites: e.g., in the Hatrurim Formation and in some burned coal dumps. The formula can be written as [Ca12Al14O32]O, which refers to the unique...

 and gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

 in the Hatrurim Formation. It has also been reported from the Zeilberg quarry, Maroldsweisach
Maroldsweisach
Maroldsweisach is a municipality in the district of Haßberge in Bavaria in Germany.-Local Citizens of Note:* Joseph Brunner was born in Trappstadt and died in Altenstein...

, Bavaria
Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

; at Boisséjour, near Clermont-Ferrand, Puy-de-Dôme
Puy-de-Dôme
Puy-de-Dôme is a department in the centre of France named after the famous dormant volcano, the Puy-de-Dôme.Inhabitants were called Puydedomois until December 2005...

, Auvergne
Auvergne (région)
Auvergne is one of the 27 administrative regions of France. It comprises the 4 departments of Allier, Puy de Dome, Cantal and Haute Loire.The current administrative region of Auvergne is larger than the historical province of Auvergne, and includes provinces and areas that historically were not...

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

; the N’Chwaning mine, Kuruman district, Cape Province
Cape Province
The Province of the Cape of Good Hope was a province in the Union of South Africa and subsequently the Republic of South Africa...

, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

; in the USA, at the Crestmore quarry, Riverside County, California
Riverside County, California
Riverside County is a county in the U.S. state of California. One of 58 California counties, it covers in the southern part of the state, and stretches from Orange County to the Colorado River, which forms the state border with Arizona. The county derives its name from the city of Riverside,...

 and in the Lucky Cuss mine, Tombstone, Cochise County, Arizona
Cochise County, Arizona
-2010:Whereas according to the 2010 U.S. Census Bureau:*78.5% White*4.2% Black*1.2% Native American*1.9% Asian*0.3% Native Hawaiian or Pacific Islander*4.0% Two or more races*9.6% Other races*32.4% Hispanic or Latino -2000:...

.

Occurrence in cement



In concrete chemistry ettringite is a hexacalcium aluminate trisulfate hydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....

, of general formula:6(Al2O3)(SO3)3·32H2O
or3(Al2O3)(CaSO4)3·32H2O.

Ettringite is formed in hydrated Portland cement
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

 system as a result of the reaction of calcium aluminate
Calcium aluminates
Calcium aluminates are a range of minerals obtained by heating calcium oxide and aluminium oxide together at high temperatures. They are encountered in the manufacture of refractories and cements....

 with calcium sulfate
Calcium sulfate
Calcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...

, both present in Portland cement.

Ettringite, the more prominent representative of AFt phases or (Al2O3-Fe2O3-tri), can also be synthesized in the laboratory by reacting stoichiometric amounts of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

, aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 and sulfate in water.
C3A + 3 CaSO4 → ettringite


In the cement system, the presence of ettringite depends on the ratio
Ratio
In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 of calcium sulfate to tri-calcium aluminate (C3A); when this ratio is low, ettringite forms during early hydration and then converts to the calcium aluminate monosulfate (AFm phase
AFm phase
An AFm phase is an "alumina, ferric oxide, monosulfate" phase. AFm phases are important in the hydration of hydraulic cements.They are crystalline hydrates with general, simplified formula 3 CaO·2O3·CaSO4·nH2O....

 or (Al2O3-Fe2O3-mono)). When the ratio is intermediate, only a portion of the ettringite converts to AFm and both can coexist, while ettringite is unlikely to convert to AFm at high ratios.

The characters designate standard notations:
C = CaO
S = SiO2
A = Al2O3
F = Fe2O3
S̅ = SO3
H = H2O
K = K2O
N = Na2O
m = mono
t = tri

AFt and AFm phases

  • AFt: abbreviation for "alumina, ferric oxide, tri-sulfate" or (Al2O3 – Fe2O3 – tri). It represents a group of calcium sulfoaluminate hydrates. AFt has the general formula [Ca3(Al,Fe)(OH)6·12 H2O]2·X3·nH2O where X represents a doubly charged anion or, sometimes, two singly charged anions. Ettringite is the most common and important member of the AFt group (X in this case denoting sulfate).
  • AFm
    AFm phase
    An AFm phase is an "alumina, ferric oxide, monosulfate" phase. AFm phases are important in the hydration of hydraulic cements.They are crystalline hydrates with general, simplified formula 3 CaO·2O3·CaSO4·nH2O....

    : abbreviation for "Alumina, Ferric oxide, mono-sulfate" or (Al2O3 – Fe2O3 – mono). It represents another group of calcium aluminate hydrates with general formula [Ca2(Al,Fe)(OH)6)]·X·nH2O where X represents a singly charged anion or 'half' a doubly charged anion. X may be one of many anions. The most important anions involved in Portland cement hydration are hydroxyl, sulfate and carbonate.