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Ettringite

A valid IMA mineral species - grandfathered
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About EttringiteHide

Formula:
Ca6Al2(SO4)3(OH)12 · 26H2O
Colour:
Colourless; colourless in transmitted light; yellow
Hardness:
2 - 2½
Specific Gravity:
1.77
Crystal System:
Trigonal
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). Further work showed a miscibility gap in the solid solution (Barnett et al., 2003): ettringite can accept the replacement of 1/2 its Al by Si, while thaumasite tolerates little or no Al in its structure.

The Al analogue of bentorite. The S (sulfate) analogue of siwaqaite.

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




Unique IdentifiersHide

Mindat ID:
1414
Long-form identifier:
mindat:1:1:1414:0

IMA Classification of EttringiteHide

Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Ca6Al2(S6+O4)3(OH)12·27H2O

Classification of EttringiteHide

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
31.10.2.1

31 : HYDRATED SULFATES CONTAINING HYDROXYL OR HALOGEN
10 : Miscellaneous
25.4.13

25 : Sulphates
4 : Sulphates of Ca, Sr and Ba

Mineral SymbolsHide

As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.

SymbolSourceReference for Standard
EttIMA–CNMNCWarr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43

Pronunciation of EttringiteHide

Pronunciation:
PlayRecorded byCountry
Jolyon RalphUnited Kingdom

Physical Properties of EttringiteHide

Transparency:
Transparent
Colour:
Colourless; colourless in transmitted light; yellow
Comment:
Turns white upon partial dehydration.
Hardness:
2 - 2½ on Mohs scale
Cleavage:
Perfect
On {1010}, perfect.
Density:
1.77 g/cm3 (Measured)    1.76 g/cm3 (Calculated)

Optical Data of EttringiteHide

Type:
Uniaxial (-)
RI values:
nω = 1.491 nε = 1.47
Max. Birefringence:
δ = 0.021
Based on recorded range of RI values above.

Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.

Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.

Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.

Surface Relief:
Moderate (negative)
Relative to Canada balsam mounting medium (n ≈ 1.537).

This shows the grain boundary and Becke line effect under plane-polarised light, based on the contrast between this mineral's average refractive index and the mounting medium. It does not take into account mineral colouration.
In focus
Interference Figure:
This shows the idealized uniaxial interference figure - the conoscopic (convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis centred and vertical. The coloured rings are isochromatics, computed with the same physics as the Michel-Lévy bar above; the dark cross is the isogyre.

For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
Comments:
Becomes uniaxial positive on dehydration.

Chemistry of EttringiteHide

Mindat Formula:
Ca6Al2(SO4)3(OH)12 · 26H2O
Element Weights:
Element% weight
O63.737 %
Ca19.159 %
S7.664 %
H5.140 %
Al4.300 %

Calculated from ideal end-member formula.
O
Ca
S
H
Al

Crystallography of EttringiteHide

Crystal System:
Trigonal
Class (H-M):
3m - Ditrigonal Pyramidal
Space Group:
P31c
Cell Parameters:
a = 11.23 Å, c = 21.44 Å
Ratio:
a:c = 1 : 1.909
Unit Cell V:
2,341.61 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Crystals small and prismatic [0001], commonly without terminal faces.

Crystal StructureHide

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IDSpeciesReferenceLinkYearLocalityPressure (GPa)Temp (K)
0020840EttringiteGatta G D, Halenius U, Bosi F, Canadillas-Delgado L, Fernandez-Diaz M T (2019) Minerals in cement chemistry: A single-crystal neutron diffraction study of ettringite, Ca6Al2(SO4)3(OH)12?27H2O American Mineralogist 104 73-782019NChwaning mine, Kuruman, South Africa0293
0017886EttringiteGoetz-Neunhoeffer F, Neubauer J (2006) Refined ettringite (Ca6Al2(SO4)3(OH)12*26H2O) structure for quantitative X-ray diffraction analysis Powder Diffraction 21 4-112006synthetic0293
0012178EttringiteHartman M R, Berliner R (2006) Investigation of the structure of ettringite by time-of-flight neutron powder diffraction techniques Cement and Concrete Research 36 364-3702006synthetic0293
0009368EttringiteMoore A E, Taylor H F W (1970) Crystal structure of ettringite Acta Crystallographica B26 386-3931970Scawt Hill, Northern Ireland0293
0014674EttringiteMoore A, Taylor H F W (1968) Crystal structure of ettringite Nature 218 1048-10491968Scawt Hill, Northern Ireland0293
CIF Raw Data - click here to close

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
9.73 Å(100)
5.61 Å(80)
3.88 Å(50)
2.564 Å(45)
2.209 Å(45)
2.773 Å(40)
4.69 Å(35)
Comments:
Synthetic.

Geological EnvironmentHide

Paragenetic Mode(s):
Paragenetic ModeEarliest Age (Ga)
High-𝑇 alteration and/or metamorphism
31 : Thermally altered carbonate, phosphate, and iron formations
Stage 7: Great Oxidation Event<2.4
47a : [Near-surface hydration of prior minerals]
47b : [Sulfates and sulfites]
Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere<0.6
51 : Pyrometamorphic minerals (see also #54 and #56)<0.36

Type Occurrence of EttringiteHide

Place of Conservation of Type Material:
No designated type material.
Geological Setting of Type Material:
In cavities of metamorphosed limestone inclusions in a leucite-nepheline-tephrite rock.

Synonyms of EttringiteHide

Other Language Names for EttringiteHide

Simplified Chinese:钙钒石
Spanish:Ettringita

Relationship of Ettringite to other SpeciesHide

Other Members of Ettringite Group:
BentoriteCa6Cr2(SO4)3(OH)12 · 26H2OTrig. 3m : P31c
BuryatiteCa3(Si,Fe3+,Al)(SO4)B(OH)4(OH,O)6 · 12H2OTrig. 3m : P31c
CarraraiteCa3(SO4)[Ge(OH)6](CO3) · 12H2OHex.
CharlesiteCa6(Al,Si)2(SO4)2[B(OH)4](OH,O)12 · 26H2OTrig. 3m : P31c
ChiyokoiteCa3Si(CO3)[B(OH)4]O (OH)5 · 12H2OHex. 6 : P63
HielscheriteCa3Si(SO4)(SO3)(OH)6 · 11H2OHex. 6 : P63
ImayoshiiteCa3Al(CO3)[B(OH)4](OH)6 · 12H2OHex. 6/mmm(6/m2/m2/m) : P63/mmc
JouravskiteCa3Mn4+(SO4)(CO3)(OH)6 · 12H2OHex. 6 : P63
KottenheimiteCa 3Si(SO4)2(OH)6 · 12H2O Hex. 6/m : P63/m
Micheelsenite(Ca2Y)Al(PO3OH)(CO3)(OH)6 · 12H2OHex. 6 : P63
SiwaqaiteCa6Al2(CrO4)3(OH)12 · 26H2OTrig. 3m : P31c
SturmaniteCa6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25H2OTrig. 3m : P31c
TatarinoviteCa3Al(SO4)[B(OH)4](OH)6 · 12H2OHex. 6 : P63
ThaumasiteCa3(SO4)[Si(OH)6](CO3) · 12H2OHex. 6 : P63
'UM2008-07-CO:AlBCaHSSi'Ca6(Al,Si)2(CO3,SO4)2[B(OH)4](OH,O)12 · 26H2O
'Unnamed (possible Mn(IV) analogue of Sturmanite)'Ca6Mn4+2(SO4)2[B(OH)4](OH)10O2 · nH2O

Common AssociatesHide

Associations Based on Photo Data:
114 photos of Ettringite associated with CalciteCaCO3
56 photos of Ettringite associated with OyeliteCa10Si8B2O29 · 12.5H2O
37 photos of Ettringite associated with HausmanniteMn2+Mn3+2O4
33 photos of Ettringite associated with GaudefroyiteCa4Mn3+2-3(BO3)3(CO3)(O,OH)3
32 photos of Ettringite associated with HematiteFe2O3
29 photos of Ettringite associated with SturmaniteCa6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25H2O
28 photos of Ettringite associated with HashemiteBaCr6+O4
25 photos of Ettringite associated with GypsumCaSO4 · 2H2O
25 photos of Ettringite associated with ManganiteMn3+O(OH)
20 photos of Ettringite associated with AfwilliteCa3[SiO4][SiO2(OH)2] · 2H2O

Related Minerals - Strunz-mindat GroupingHide

7.DG.MathesiusiteK5(UO2)4(SO4)4(VO5) · 4H2OTet. 4/m : P4/n
7.DG.05DarapskiteNa3(SO4)(NO3) · H2OMon. 2/m : P21/m
7.DG.10Clinoungemachite(Na, K, Fe, SO4)Mon. 2/m
7.DG.10HumberstoniteNa7K3Mg2(SO4)6(NO3)2 · 6H2OTrig. 3 : R3
7.DG.10UngemachiteK3Na8Fe(SO4)6(NO3)2 · 6H2OTrig. 3 : R3
7.DG.15ChiyokoiteCa3Si(CO3)[B(OH)4]O (OH)5 · 12H2OHex. 6 : P63
7.DG.15KottenheimiteCa 3Si(SO4)2(OH)6 · 12H2O Hex. 6/m : P63/m
7.DG.15HielscheriteCa3Si(SO4)(SO3)(OH)6 · 11H2OHex. 6 : P63
7.DG.15JouravskiteCa3Mn4+(SO4)(CO3)(OH)6 · 12H2OHex. 6 : P63
7.DG.15ThaumasiteCa3(SO4)[Si(OH)6](CO3) · 12H2OHex. 6 : P63
7.DG.15BentoriteCa6Cr2(SO4)3(OH)12 · 26H2OTrig. 3m : P31c
7.DG.15CarraraiteCa3(SO4)[Ge(OH)6](CO3) · 12H2OHex.
7.DG.15BiruniteCa18(SiO3)8.5(CO3)8.5SO4 · 15H2O(?)
7.DG.15SiwaqaiteCa6Al2(CrO4)3(OH)12 · 26H2OTrig. 3m : P31c
7.DG.15BuryatiteCa3(Si,Fe3+,Al)(SO4)B(OH)4(OH,O)6 · 12H2OTrig. 3m : P31c
7.DG.15CharlesiteCa6(Al,Si)2(SO4)2[B(OH)4](OH,O)12 · 26H2OTrig. 3m : P31c
7.DG.15TatarinoviteCa3Al(SO4)[B(OH)4](OH)6 · 12H2OHex. 6 : P63
7.DG.15ImayoshiiteCa3Al(CO3)[B(OH)4](OH)6 · 12H2OHex. 6/mmm(6/m2/m2/m) : P63/mmc
7.DG.15SturmaniteCa6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25H2OTrig. 3m : P31c
7.DG.20RapidcreekiteCa2(SO4)(CO3) · 4H2OOrth. mmm(2/m2/m2/m) : Pbcn
7.DG.25TatarskiteCa6Mg2(SO4)2(CO3)2(OH)4Cl4 · 7H2OOrth.
7.DG.30NakauriiteCu8(SO4)4(CO3)(OH)6 · 48H2OOrth.
7.DG.35Chessexite(Na,K)4Ca2(Mg,Zn)3Al8(SO4)10(SiO4)2 · 40H2OOrth.
7.DG.40FuenzalidaiteK6(Na,K)4Na6Mg10(SO4)12(IO3)12 · 12H2OTrig. 3m(32/m) : P3c1
7.DG.40CarlosruiziteK6(Na,K)4Na6Mg10(SeO4)12(IO3)12 · 12H2OTrig. 3m(32/m) : P3c1
7.DG.45'Chelyabinskite'(Ca,Mg)3(SO4,CO3)2[Si(OH)6] · 9H2O (?)Orth.
7.DG.55Ramazzoite[Mg8Cu12(PO4)(CO3)4(OH)24(H2O)20][(H0.33SO4)3(H2O)36]Iso. 43m : P43m
7.DG.60WitzkeiteNa4K4Ca(NO3)2(SO4)4 · 2H2O Mon. 2/m : B2/b

Other InformationHide

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

Internet Links for EttringiteHide

References for EttringiteHide

Reference List:

Localities for EttringiteHide

Showing 135 localities.

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.
Austria
 
  • Lower Austria
    • Melk District
      • Persenbeug-Gottsdorf
        • Loja
Löffler et al. (2011)
    • Neunkirchen District
      • Gloggnitz
Kolitsch et al. (2017)
  • Styria
    • Leoben District
      • Eisenerz
Kolitsch (2016)
      • Leoben
        • Galgenberg
Hollerer (1999)
    • Murtal District
      • Weißkirchen in Steiermark
        • Kleinfeistritz
          • Kothgraben (Kotgraben)
C.Auer (2012)
    • Südoststeiermark District
      • Bad Gleichenberg
        • Wilhelmsdorf
Postl et al. (1996)
      • Klöch
Postl et al. (1983) +1 other reference
  • Tyrol
    • Kufstein District
      • Reith im Alpbachtal
        • St Gertraudi
- (1994, July)
  • Upper Austria
    • Steyr
      • Slag localities
G Brandstetter collection
Neschen (n.d.)
Belgium
 
  • Flanders
    • Limburg
      • Dilsen-Stokkem
        • Rotem
  • Wallonia
    • Namur
      • Andenne
        • Seilles
France
 
  • Auvergne-Rhône-Alpes
    • Loire
      • Roanne
        • Le Crozet
Chollet et al. (2013)
    • Puy-de-Dôme
      • Clermont-Ferrand
        • Beaumont
Grünhagen et al. (1963) +1 other reference
        • Ceyrat
  • Occitanie
    • Aveyron
      • Rodez
        • Espalion
Boutry et al. (1986)
        • Sévérac-d'Aveyron
Eytier J.R. & Ch. et al. (2004)
Germany
 
  • Baden-Württemberg
    • Freiburg Region
      • Ortenaukreis
        • Oberwolfach
Walenta (1992)
  • Bavaria
    • Lower Bavaria
      • Passau District
        • Hauzenberg
          • Kropfmühl
Habel (2011)
    • Lower Franconia
      • Haßberge District
        • Maroldsweisach
Pöllmann (1991)
  • Hesse
    • Kassel Region
      • Hersfeld-Rotenburg
        • Nentershausen
          • Süß
            • Richelsdorf Smelter
Weiß (1990)
  • Lower Saxony
    • Goslar District
      • Langelsheim
        • Lautenthal
Luetcke (n.d.)
Neschen (n.d.)
Luetcke (n.d.)
    • Osnabrück District
      • Georgsmarienhütte
Schnorrer et al. (2001)
  • North Rhine-Westphalia
    • Arnsberg
      • Hochsauerlandkreis
        • Arnsberg
          • Hüsten
Weiß (1990)
      • Märkischer Kreis
        • Iserlohn
          • Letmathe
            • Helmke quarry nature reserve
Bender et al. (1994) +1 other reference
      • Siegen-Wittgenstein
        • Siegen
          • Geisweid
Neschen (n.d.)
    • Cologne
      • Aachen
        • Eschweiler
        • Stolberg
Neschen (n.d.)
International Association of Collectors ... +1 other reference
      • Euskirchen
        • Kall
Blaß et al. (1995)
  • Rhineland-Palatinate
    • Ahrweiler
      • Brohltal
        • Brenk
Hentschel (1968) +1 other reference
    • Mayen-Koblenz
      • Mayen
Lehmann (1874)
Peacor et al. (1984)
in the collection of Christof Schäfer
Skrzyńska et al. (2023)
Juroszek et al. (Ti 5 Fe)
      • Mendig
        • Bell
Hentschel (1983)
        • Mendig
Hentschel (1983)
      • Vordereifel
        • Ettringen
Hentschel (1983)
Juroszek et al. (2024)
Galuskin et al. (2016)
in the collection of Christof Schäfer
in the collection of Christof Schäfer
in the collection of Christof Schäfer
Lehmann (1874)
        • Kottenheim
Hentschel (1983)
Lehmann (1874)
    • Rhein-Lahn-Kreis
Wittern (2001)
      • Lahnstein
        • Friedrichssegen
Der Aufschluss Vol.55
      • Loreley
        • Braubach
58 (in German) +1 other reference
    • Vulkaneifel
      • Daun
        • Üdersdorf
Hentschel (1983)
      • Gerolstein
        • Gerolstein
          • Roth
Blaß et al. (2012)
        • Hillesheim
G. Blaß
        • Hohenfels-Essingen
Blass et al. (2006)
  • Saarland
    • Saarlouis
      • Dillingen/Saar
Thomas Kleser Collection
  • Saxony-Anhalt
    • Salzlandkreis
      • Börde-Hakel
        • Westeregeln
mikon-online.com (n.d.)
  • Saxony
    • Erzgebirgskreis
      • Marienberg
        • Lauta
Hajek (2010)
  • Thuringia
    • Greiz District
      • Kauern
Witzke et al. (1998)
Greece
 
  • Attica
    • East Attica
      • Lavreotiki
        • Charakas
Gelaude et al. (1996)
        • Lavreotiki Municipal Unit
Gelaude et al. (1996)
Schnorrer-Köhler et al. (1988)
        • Sounion