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Ettringite

Big Photo

Caspar quarry, Ettringer Bellerberg Mt. (Bellberg Mt.; Bellenberg Mt.; Billenberg Mt.; Boilenberg Mt.), Bellerberg volcano, Ettringen, Mayen, Eifel Mts, Rhineland-Palatinate, Germany
© Stephan Wolfsried

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Formula:
Ca
 
6
Al
 
2
[(OH)
 
4
|SO
 
4
]
 
3
 · 26H
 
2
O
System:TrigonalColour:Colourless; colourless ...
Hardness:2 - 2½
Name:After the type locality at Ettringen, Rhineland-Palatinate, Germany.


Ettringite Group.

Although it is generally assumed that a solid solution series between ettringite and thaumasite exists, both species have different space groups and a possible discontinuity was identified, characterised by a gap in the a-dimension of the solid solution phases (Barnett et al., 2000).

Well-known as a synthetic phase in concrete.
Has been discussed as a potential phase for immobilisation of toxic metals.

Classification of Ettringite

IMA status:Approved
Strunz 8th edition ID:6/D.13-10
Strunz 9th edition ID:7.DG.15
Nickel-Strunz 10th (pending) edition ID:7.DG.15

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
D : Sulfates (selenates, etc.) with additional anions, with H2O
G : With large and medium-sized cations; with NO3, CO3, B(OH)4, SiO4 or IO3
Dana 8th edition ID:31.10.2.1

31 : HYDRATED SULFATES CONTAINING HYDROXYL OR HALOGEN
10 : Miscellaneous
Hey's CIM Ref.:25.4.13

25 : Sulphates
4 : Sulphates of Ca, Sr and Ba
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Type Occurrence of Ettringite

Co-type Localities:Mayener Feld, Southern lava flow, Bellerberg volcano, Ettringen, Mayen, Eifel Mts, Rhineland-Palatinate, Germany
Ettringer Feld, Western lava flow, Bellerberg volcano, Ettringen, Mayen, Eifel Mts, Rhineland-Palatinate, Germany
Year of Discovery:1874
Geological Setting of type material:In cavities of metamorphosed limestone inclusions in a leucite-nepheline-tephrite rock.

Physical Properties of Ettringite

Diaphaneity (Transparency):Transparent
Colour:Colourless; colourless in transmitted light.
Comment:Turns white upon partial dehydration.
Hardness (Mohs):2 - 2½
Cleavage:Perfect
On {10_10}, perfect.
Density (measured):1.77 g/cm3
Density (calculated):1.76 g/cm3

Crystallography of Ettringite

Crystal System:Trigonal
Class (H-M):3m - Ditrigonal Pyramidal
Space Group:P3 1c
Cell Parameters:a = 11.23Å, c = 21.44Å
Ratio:a:c = 1 : 1.909
Unit Cell Volume:V 2,341.61 ų (Calculated from Unit Cell)
Z:2
Morphology:Crystals small and prismatic [0001], commonly without terminal faces.

Optical Data of Ettringite

Type:Uniaxial (-)
RI values: nω = 1.491 nε = 1.470
Maximum Birefringence:δ = 0.021

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Moderate
Comments:Becomes uniaxial positive on dehydration.

Chemical Properties of Ettringite

Formula:
Ca
 
6
Al
 
2
[(OH)
 
4
|SO
 
4
]
 
3
 · 26H
 
2
O
Essential elements:Al, Ca, H, O, S
All elements listed in formula:Al, Ca, H, O, S

Relationship of Ettringite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
7.DG.05Darapskite
Na
 
3
NO
 
3
SO
 
4
·H
 
2
O
7.DG.10Clinoungemachite
(Na, K, Fe, SO
 
4
)
7.DG.10Humberstonite
Na
 
7
K
 
3
Mg
 
2
(SO
 
4
)
 
6
(NO
 
3
)
 
2
·6H
 
2
O
7.DG.10Ungemachite
K
 
3
Na
 
8
Fe(SO
 
4
)
 
6
(NO
 
3
)
 
2
·6H
 
2
O
7.DG.15Bentorite
Ca
 
6
(Cr
3+
 
,Al)
 
2
[(OH)
 
4
|SO
 
4
]
 
3
 · 26H
 
2
O
7.DG.15Charlesite
Ca
 
6
(Al,Si)
 
2
[(OH,O)
 
12
|B(OH)
 
4
|(SO
 
4
)
 
2
] · 26H
 
2
O
7.DG.15Jouravskite
Ca
 
6
Mn
3+
2
[(OH)
 
4
|(SO
 
4
,CO
 
3
)]
 
3
 · 26H
 
2
O
7.DG.15Sturmanite
Ca
 
6
(Fe
3+
 
,Al,Mn
3+
 
)
 
2
[(OH)
 
12
|B(OH)
 
4
|(SO
 
4
)
 
2
] · 25H
 
2
O
7.DG.15Thaumasite
Ca
 
3
[CO
 
3
|SO
 
4
|Si(OH)
 
6
] · 12H
 
2
O
7.DG.15Carraraite
Ca
 
3
Ge(OH)
 
6
(SO
 
4
)(CO
 
3
)·12H
 
2
O
7.DG.15Buryatite
Ca
 
3
(Si,Fe,Al)[SO
 
4
][B(OH)
 
4
](OH)
 
5
O•
 
12
H
 
2
O
7.DG.20Rapidcreekite
Ca
 
2
[CO
 
3
|SO
 
4
] · 4H
 
2
O
7.DG.20Korkinoite
Ca, SO
 
4
, H
 
2
O reported
7.DG.25Tatarskite
Ca
 
6
Mg
 
2
(SO
 
4
)
 
2
(CO
 
3
)
 
2
Cl
 
4
(OH)
 
4
·7H
 
2
O
7.DG.30Nakauriite
Cu
 
8
[(OH)
 
6
|CO
 
3
|(SO
 
4
)
 
4
] · 48H
 
2
O
7.DG.35Chessexite
(Na,K)
 
4
Ca
 
2
(Mg,Zn)
 
3
Al
 
8
[(SO
 
4
)
 
10
|(SiO
 
4
)
 
2
] · 40H
 
2
O
7.DG.40Carlosruizite
K
 
6
(Na,K)
 
4
Na
 
6
Mg
 
10
(SeO
 
4
)
 
12
(IO
 
3
)
 
12
·12H
 
2
O
7.DG.40Fuenzalidaite
K
 
6
(Na,K)
 
4
Na
 
6
Mg
 
10
(SO
 
4
)
 
12
(IO
 
3
)
 
12
·12H
 
2
O
7.DG.45Chelyabinskite
(Ca,Mg)
 
3
[(SO
 
4
,CO
 
3
)
 
2
|Si(OH)
 
6
] · 9H
 
2
O (?)
Related Minerals - Hey's Index Grouping:

- +
25.4.1Anhydrite
CaSO
 
4
25.4.2Bassanite
Ca[SO
 
4
] · 0.5H
 
2
O
25.4.3Gypsum
Ca[SO
 
4
] · 2H
 
2
O
25.4.4Glauberite
Na
 
2
Ca(SO
 
4
)
 
2
25.4.5Cesanite
Na
 
3
Ca
 
2
[OH|(SO
 
4
)
 
3
]
25.4.6Eugsterite
Na
 
4
Ca(SO
 
4
)
 
3
·2H
 
2
O
25.4.7Hydroglauberite
Na
 
10
Ca
 
3
(SO
 
4
)
 
8
·6H
 
2
O
25.4.8Syngenite
K
 
2
Ca(SO
 
4
)
 
2
·H
 
2
O
25.4.9Görgeyite
K
 
2
Ca
 
5
(SO
 
4
)
 
6
·H
 
2
O
25.4.10Polyhalite
K
 
2
Ca
 
2
Mg(SO
 
4
)
 
4
·2H
 
2
O
25.4.11Koktaite
(NH
 
4
)
 
2
Ca(SO
 
4
)
 
2
·H
 
2
O
25.4.12Ye'elimite
Ca
 
4
Al
 
6
[O
 
12
|SO
 
4
]
25.4.14Bentorite
Ca
 
6
(Cr
3+
 
,Al)
 
2
[(OH)
 
4
|SO
 
4
]
 
3
 · 26H
 
2
O
25.4.15Celestine
SrSO
 
4
25.4.16Kalistrontite
K
 
2
Sr(SO
 
4
)
 
2
25.4.17Baryte
BaSO
 
4

Other Names for Ettringite

Synonyms:
Woodfordite
Other Languages:
German:Chalkomorphit
Ettringit
Russian:Эттрингит
Spanish:Ettringita

Other Information

Other Information:Readily soluble in dilute acids. Partially decomposed by water, rendering an alkaline solution.
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Ettringite

Reference List:Vom Rath, G. (1873): Über ein neues Mineral (Chalkomorphit) auf einem Einschluß in der Lava von Niedermendig, Annalen der Chemie und Physik, Ergänzungsband VI, 376-378

Lehmann, J. (1874): Untersuchungen über die Einwirkung eines feurig-flüssigen basaltischen Magmas auf Gesteins- und Mineraleinschlüsse, Verhandlungen des naturhistorischen Vereins der preußischen Rheinlande und Westfalens, Vol. 31, Cohen Bonn, p 1-40

Lehmann, J. (1874): "Über den Ettringit, ein neues Mineral in Kalkeinschlüssen der Lava von Ettringen (Laacher Gebiet)", N. Jb. Mineral. Geol. Paläont., 273-275.

Moses (1893) American Journal of Science: 45: 489.

Brauns, R.A. (1922) Die Mineralien der niederrheinischen Vulkangebiete. 225pp., 4to, Stuttgart: 173.

Bannister, M.A. (1935): Ettringite from Scawt Hill, Co. Antrim, Mineralogical Magazin, Vol. 24, 324-329.


Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 589-590.

McConnell, Duncan & Joseph Murdoch (1962): Crystal chemistry of ettringite. Mineralogical Magazine: 33: 59-64.

Carpenter, A.B. (1963): Oriented overgrowths of thaumasite on ettringite. Am. Mineral. 48, 1394–1396.

McCarthy, Gregory J.; Hassett, David J.; Bender, Jason A. (1992): Synthesis, crystal chemistry and stability of ettringite, a material with potential applications in hazardous waste immobilization. Mater. Res. Soc. Symp. Proc. 245, 129-140.

Barnett, S.J., Adam, C.D. & Jackson, A.R.W. (2000): Solid solutions between ettringite and thaumasite. Journal of Materials Science 35, 4109-4114.

Barnett, S.J., Adam, C.D. & Jackson, A.R.W. (2001): An XRPD profile fitting investigation of the solid solution between ettringite, Ca6Al2(SO4)3(OH)12.26H2O and carbonate ettringite, Ca6Al2(CO3)3(OH)12.26H2O. Cement and Concrete Research, 31, 13-17.

Goetz-Neunhoeffer, F. and Neubauer, J. (2006): Refined ettringite (Ca6Al2(SO4)3(OH)12•26H2O) structure for quantitative X-ray diffraction analysis. Powder Diffr. 21, 4-11.

Internet Links for Ettringite

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    Localities for Ettringite

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