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Montmorillonite

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Formula:
(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O
Colour:
White, buff, yellow, green, rarely pale pink to red
Lustre:
Dull, Earthy
Hardness:
1 - 2
Specific Gravity:
2 - 3
Crystal System:
Monoclinic
Member of:
Name:
For the type locality at Montmorillon, Vienne, Poitou-Charentes, France.
Montmorillonite-Vermiculite Group; Beidellite-Montmorillonite Series.

A common clay mineral. Compare 'UM1979-21-SiO:AlHNaV'.

As halloysite, it may be a biomineral formed by the action of lichens (e.g., Lasallia spp., Parmelia spp., etc.) on cave deposits and waters (vide Burford et al., 2003).


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Classification of MontmorilloniteHide

Approved, 'Grandfathered' (first described prior to 1959)
9.EC.40

9 : SILICATES (Germanates)
E : Phyllosilicates
C : Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets
71.3.1a.2

71 : PHYLLOSILICATES Sheets of Six-Membered Rings
3 : Sheets of 6-membered rings with 2:1 clays
16.7.9

16 : Silicates Containing Aluminum and other Metals
7 : Aluminosilicates of Mg

Physical Properties of MontmorilloniteHide

Dull, Earthy
Transparency:
Translucent
Comment:
Low luster because of fine-grained nature of the mineral
Colour:
White, buff, yellow, green, rarely pale pink to red
Comment:
Pink to red coloration is due to high valance Mn
Streak:
white
Hardness:
1 - 2 on Mohs scale
Comment:
Soft because of fine-grained occurrence
Cleavage:
Perfect
on {001}
Fracture:
Irregular/Uneven
Density:
2 - 3 g/cm3 (Measured)    

Optical Data of MontmorilloniteHide

Type:
Biaxial (-)
RI values:
nα = 1.485 - 1.535 nβ = 1.504 - 1.550 nγ = 1.505 - 1.550
2V:
Measured: 5° to 30°
Birefringence:
0.02
Max Birefringence:
δ = 0.020
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
Low
Dispersion:
none
Pleochroism:
Visible
Comments:
X= colorless to pale brown, yellow green
Y= dark brown to yellow-green, olive-green, pale yellow
Z= brown to olive-green, pale yellow
Comments:
Usually not pleochroic; pleochroism dependent on chemical substitution

Chemical Properties of MontmorilloniteHide

Formula:
(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O
IMA Formula:
(Na,Ca)0.3(Al,Mg)2Si4O10(OH)2 · nH2O
Common Impurities:
Fe,K

Crystallography of MontmorilloniteHide

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/m
Cell Parameters:
a = 5.17 Å, b = 8.94 Å, c = 9.95 Å
β = 99.54°
Ratio:
a:b:c = 0.578 : 1 : 1.113
Unit Cell V:
453.53 ų (Calculated from Unit Cell)
Z:
1
Morphology:
Scaly crystals, clayey, compact, massive

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
15.0 (100)
5.01 (60)
4.50 (80)
3.77 (20)
3.02 (60)
1.70 (30)
1.50 (50)
1.49 (50)
Comments:
Basal spacings sensitive to interlayer hydration. Dehydrated montmorillonite may have a 13.6 Angstrom spacing.

Type Occurrence of MontmorilloniteHide

General Appearance of Type Material:
Compact earthy massive mineral.

Synonyms of MontmorilloniteHide

Other Language Names for MontmorilloniteHide

Varieties of MontmorilloniteHide

AlumodeweyliteAn intermediate between montmorillonite and sepiolite.
AskaniteA variety of Montmorillonite - a decomposition product of volcanic ash.

Originally described from Askana, Ozurgety District, Georgia.
BatrachiteA pale greenish-grey variety of Montmorillonite.

Originally reported from Toal de Rizzoni, Monzoni Mts, Fassa Valley, Trento Province, Trentino-Alto Adige, Italy.
Calcium-MontmorilloniteA calcian montmorillonite
DelanoviteA manganiferous variety of Montmorillonite.
Originally reported from Dordogne, Aquitaine, France.

Relationship of Montmorillonite to other SpeciesHide

Member of:
Other Members of this group:
AliettiteCa0.2Mg6((Si,Al)8O20)(OH)4 · 4H2OMon.
Beidellite(Na,Ca0.5)0.3Al2((Si,Al)4O10)(OH)2 · nH2OMon.
FerrosaponiteCa0.3(Fe2+,Mg,Fe3+)3((Si,Al)4O10)(OH)2 · 4H2O
HectoriteNa0.3(Mg,Li)3(Si4O10)(F,OH)2Mon.
NontroniteNa0.3Fe2((Si,Al)4O10)(OH)2 · nH2OMon.
PimeliteNi3Si4O10(OH)2·4H2OHex.
Saliotite(Li,Na)Al3(AlSi3O10)(OH)5Mon.
SaponiteCa0.25(Mg,Fe)3((Si,Al)4O10)(OH)2 · nH2OMon.
SauconiteNa0.3Zn3((Si,Al)4O10)(OH)2 · 4H2OMon.
Stevensite(Ca,Na)xMg3-x(Si4O10)(OH)2Mon.
SwineforditeLi(Al,Li,Mg)4((Si,Al)4O10)2(OH,F)4 · nH2OMon.
VolkonskoiteCa0.3(Cr,Mg,Fe)2((Si,Al)4O10)(OH)2 · 4H2OMon.
Yakhontovite(Ca,Na)0.5(Cu,Fe,Mg)2(Si4O10)(OH)2 · 3H2OMon.
ZincsiliteZn3(Si4O10)(OH)2 · 4H2OMon.
Structurally related to group(s):
Forms a series with:

Common AssociatesHide

Associated Minerals Based on Photo Data:
Quartz45 photos of Montmorillonite associated with Quartz on mindat.org.
Elbaite9 photos of Montmorillonite associated with Elbaite on mindat.org.
Cleavelandite9 photos of Montmorillonite associated with Cleavelandite on mindat.org.
Siderite8 photos of Montmorillonite associated with Siderite on mindat.org.
Chabazite8 photos of Montmorillonite associated with Chabazite on mindat.org.
Lepidolite8 photos of Montmorillonite associated with Lepidolite on mindat.org.
Offretite8 photos of Montmorillonite associated with Offretite on mindat.org.
Spodumene6 photos of Montmorillonite associated with Spodumene on mindat.org.
Kunzite6 photos of Montmorillonite associated with Kunzite on mindat.org.
Petalite4 photos of Montmorillonite associated with Petalite on mindat.org.

Related Minerals - Nickel-Strunz GroupingHide

9.EC.05MinnesotaiteFe2+3Si4O10(OH)2Tric. 1 : P1
9.EC.05TalcMg3Si4O10(OH)2Tric. 1 : P1
9.EC.05WillemseiteNi3Si4O10(OH)2Mon.
9.EC.10FerripyrophylliteFe3+Si2O5(OH)Mon.
9.EC.10PyrophylliteAl2Si4O10(OH)2Tric. 1
9.EC.15BoromuscoviteKAl2(BSi3O10)(OH)2Mon.
9.EC.15CeladoniteK(Mg,Fe2+)Fe3+(Si4O10)(OH)2Mon. 2/m : B2/m
9.EC.15Chernykhite(Ba,Na)(V3+,Al,Mg)2((Si,Al)4O10)(OH)2Mon.
9.EC.15Montdorite(K,Na)2(Fe2+,Mn2+,Mg)5(Si4O10)2(OH,F)4
9.EC.15MuscoviteKAl2(AlSi3O10)(OH)2Mon. 2/m : B2/b
9.EC.15NanpingiteCsAl2(AlSi3O10)(OH,F)2Mon.
9.EC.15ParagoniteNaAl2(AlSi3O10)(OH)2Mon.
9.EC.15RoscoeliteK(V3+,Al)2(AlSi3O10)(OH)2Mon. 2/m : B2/b
9.EC.15Tobelite(NH4,K)Al2(AlSi3O10)(OH)2Mon.
9.EC.15AluminoceladoniteK(Mg,Fe2+)Al(Si4O10)(OH)2Mon.
9.EC.15ChromphylliteK(Cr,Al)2(AlSi3O10)(OH,F)2Mon. 2/m : B2/b
9.EC.15FerroaluminoceladoniteK(Fe2+,Mg)(Al,Fe3+)(Si4O10)(OH)2Mon. 2/m : B2/m
9.EC.15FerroceladoniteK(Fe2+,Mg)(Fe3+,Al)(Si4O10)(OH)2Mon. 2/m : B2/m
9.EC.15ChromceladoniteK(Mg,Fe2+)(Cr,Al)(Si4O10)(OH)2Mon.
9.EC.15TainioliteKLiMg2(Si4O10)F2Mon.
9.EC.15Ganterite(Ba,Na,K)(Al,Mg)2(AlSi3O10)(OH)2Mon.
9.EC.20AnniteKFe2+3(AlSi3O10)(OH)2Mon. 2/m : B2/m
9.EC.20EphesiteLiNaAl2(Al2Si2O10)(OH)2Tric.
9.EC.20HendricksiteK(Zn,Mg,Mn2+)3(AlSi3O10)(OH)2Mon. 2/m : B2/m
9.EC.20Masutomilite(K,Rb)(Li,Mn3+,Al)3(AlSi3O10)(F,OH)2Mon.
9.EC.20NorrishiteKLiMn3+2(Si4O10)O2Mon. 2/m : B2/m
9.EC.20PhlogopiteKMg3(AlSi3O10)(OH)2Mon. 2/m : B2/m
9.EC.20PolylithioniteKLi2Al(Si4O10)(F,OH)2Mon. 2/m : B2/b
9.EC.20PreiswerkiteNaMg2Al(Al2Si2O10)(OH)2Mon.
9.EC.20SiderophylliteKFe2+2Al(Al2Si2O10)(OH)2Mon.
9.EC.20TetraferriphlogopiteKMg3(Fe3+Si3O10)(OH,F)2
9.EC.20FluorotetraferriphlogopiteKMg3(Fe3+Si3O10)F2Mon. 2/m : B2/m
9.EC.20Wonesite(Na,K)(Mg,Fe,Al)6((Al,Si)4O10)2(OH,F)4Mon. 2/m : B2/m
9.EC.20EastoniteKMg2Al(Al2Si2O10)(OH)2Mon.
9.EC.20TetraferrianniteKFe2+3((Fe3+,Al)Si3O10)(OH)2Mon.
9.EC.20TrilithioniteK(Li1.5Al1.5)(AlSi3O10)(F,OH)2Mon. 2/m : B2/b
9.EC.20FluoranniteKFe2+3(AlSi3O10)(F,OH)2Mon.
9.EC.20ShirokshiniteKNaMg2(Si4O10)F2Mon. 2/m : B2/m
9.EC.20ShirozuliteK(Mn2+,Mg)3(AlSi3O10)(OH)2Mon. 2/m : B2/m
9.EC.20SokolovaiteCsLi2Al(Si4O10)F2Mon.
9.EC.20AspidoliteNaMg3(AlSi3O10)(OH)2Mon. 2/m : B2/m
9.EC.20FluorophlogopiteKMg3(AlSi3O10)(F,OH)2Mon. 2/m : B2/m
9.EC.20UM2004-49-SiO:AlCsFHKLi(Cs,K)(Al,Li)2.6((Si,Al)4O10)(F,OH)2
9.EC.20Suhailite(NH4)Fe2+3(AlSi3O10)(OH)2Mon. 2/m : B2/m
9.EC.20YangzhumingiteKMg2.5(Si4O10)F2Mon. 2/m : B2/m
9.EC.20OrloviteKLi2Ti(Si4O10)OFMon. 2 : B2
9.EC.20OxyphlogopiteK(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2Mon. 2/m : B2/m
9.EC.25Brammallite(Na,H3O)(Al,Mg,Fe)2((Si,Al)4O10)(OH)2Mon.
9.EC.30MargariteCaAl2(Al2Si2O10)(OH)2Mon.
9.EC.35Anandite(Ba,K)(Fe2+,Mg)3((Si,Al,Fe)4O10)(S,OH)2Mon. 2/m : B2/b
9.EC.35BityiteLiCaAl2(AlBeSi2O10)(OH)2Mon. 2/m : B2/b
9.EC.35ClintoniteCa(Mg,Al)3(Al3SiO10)(OH)2Mon. 2/m : B2/m
9.EC.35Kinoshitalite(Ba,K)(Mg,Mn2+,Al)3(Al2Si2O10)(OH)2Mon.
9.EC.35Ferrokinoshitalite(Ba,K)(Fe2+,Mg)3(Al2Si2O10)(OH,F)2Mon.
9.EC.35Oxykinoshitalite(Ba,K)(Mg,Ti,Fe3+,Fe2+)3((Si,Al)4O10)(O,OH,F)2Mon. 2/m : B2/m
9.EC.35FluorokinoshitaliteBaMg3(Al2Si2O10)F2Mon. 2/m : B2/m
9.EC.40Beidellite(Na,Ca0.5)0.3Al2((Si,Al)4O10)(OH)2 · nH2OMon.
9.EC.40Kurumsakite(Zn,Ni,Cu)8Al8V5+2Si5O35 · 27H2O (?)
9.EC.40NontroniteNa0.3Fe2((Si,Al)4O10)(OH)2 · nH2OMon.
9.EC.40VolkonskoiteCa0.3(Cr,Mg,Fe)2((Si,Al)4O10)(OH)2 · 4H2OMon.
9.EC.40Yakhontovite(Ca,Na)0.5(Cu,Fe,Mg)2(Si4O10)(OH)2 · 3H2OMon.
9.EC.45HectoriteNa0.3(Mg,Li)3(Si4O10)(F,OH)2Mon.
9.EC.45SaponiteCa0.25(Mg,Fe)3((Si,Al)4O10)(OH)2 · nH2OMon.
9.EC.45SauconiteNa0.3Zn3((Si,Al)4O10)(OH)2 · 4H2OMon.
9.EC.45SpadaiteMgSiO2(OH)2 · H2O (?)
9.EC.45Stevensite(Ca,Na)xMg3-x(Si4O10)(OH)2Mon.
9.EC.45SwineforditeLi(Al,Li,Mg)4((Si,Al)4O10)2(OH,F)4 · nH2OMon.
9.EC.45ZincsiliteZn3(Si4O10)(OH)2 · 4H2OMon.
9.EC.45FerrosaponiteCa0.3(Fe2+,Mg,Fe3+)3((Si,Al)4O10)(OH)2 · 4H2O
9.EC.50VermiculiteMg0.7(Mg,Fe,Al)6(Si,Al)8O20(OH)4 · 8H2OMon. 2/m
9.EC.55Baileychlore(Zn,Fe2+,Al,Mg)6(Si,Al)4O10(OH)8Tric.
9.EC.55Chamosite(Fe2+,Mg,Al,Fe3+)6(Si,Al)4O10(OH,O)8Mon.
9.EC.55ClinochloreMg5Al(AlSi3O10)(OH)8Mon. 2/m : B2/m
9.EC.55Cookeite(Al2Li)Al2(AlSi3O10)(OH)8Mon. 2/m
9.EC.55FranklinfurnaceiteCa2Fe3+Mn2+3Mn3+(Zn2Si2O10)(OH)8Mon. 2 : B2
9.EC.55Gonyerite(Mn2+,Mg)5Fe3+(Fe3+Si3O10)(OH)8
9.EC.55Nimite(Ni,Mg,Al)6((Si,Al)4O10)(OH)8Mon.
9.EC.55Orthochamosite(Fe2+,Mg,Fe3+)5Al(AlSi3O10)(OH,O)8
9.EC.55PennantiteMn2+5Al(AlSi3O10)(OH)8Tric.
9.EC.55SudoiteMg2Al3(Si3Al)O10)(OH)8Mon.
9.EC.55DonbassiteAl4.33(AlSi3O10)(OH)8Mon. 2 : B2
9.EC.55GlagoleviteNa(Mg,Al)6(AlSi3O10)(OH,O)8Tric. 1 : P1
9.EC.55BorocookeiteLi1+3xAl4-x(BSi3O10)(OH)8
9.EC.60AliettiteCa0.2Mg6((Si,Al)8O20)(OH)4 · 4H2OMon.
9.EC.60Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2OOrth.
9.EC.60DozyiteMg7Al2(Al2Si4O15)(OH)12Mon.
9.EC.60HydrobiotiteK(Mg,Fe2+)6((Si,Al)8O20)(OH)4 · nH2OMon.
9.EC.60Karpinskite(Ni,Mg)2Si2O5(OH)2 (?)
9.EC.60KulkeiteMg8Al(AlSi7O20)(OH)10Mon.
9.EC.60LunijianlaiteLi0.7Al6.2(AlSi7O20)(OH,O)10Mon.
9.EC.60Rectorite(Na,Ca)Al4((Si,Al)8O20)(OH)4 · 2H2OMon.
9.EC.60Saliotite(Li,Na)Al3(AlSi3O10)(OH)5Mon.
9.EC.60TosuditeNa0.5(Al,Mg)6((Si,Al)8O18)(OH)12 · 5H2OMon. 2 : B2
9.EC.60BrinrobertsiteNa0.3Al4(Si4O10)2(OH)4 · 3.5 H2OMon.
9.EC.65Macaulayite(Fe,Al)24Si4O43(OH)2Mon.
9.EC.70BurckhardtitePb2(Fe3+Te6+)[AlSi3O8]O6Trig. 3m (3 2/m) : P3 1m
9.EC.75Ferrisurite(Pb,Ca)2.4Fe3+2(Si4O10)(CO3)1.7(OH)3 · nH2OMon.
9.EC.75Surite(Pb,Ca)3(Al,Fe2+,Mg)2((Si,Al)4O10)(CO3)2(OH)2Mon.
9.EC.75Niksergievite(Ba,Ca)2Al3(AlSi3O10)(CO3)(OH)6 · nH2OMon.
9.EC.80KegelitePb8Al4(Si8O20)(SO4)2(CO3)4(OH)8Mon.

Related Minerals - Dana Grouping (8th Ed.)Hide

71.3.1a.1Beidellite(Na,Ca0.5)0.3Al2((Si,Al)4O10)(OH)2 · nH2OMon.
71.3.1a.3NontroniteNa0.3Fe2((Si,Al)4O10)(OH)2 · nH2OMon.
71.3.1a.4VolkonskoiteCa0.3(Cr,Mg,Fe)2((Si,Al)4O10)(OH)2 · 4H2OMon.
71.3.1a.5SwineforditeLi(Al,Li,Mg)4((Si,Al)4O10)2(OH,F)4 · nH2OMon.

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

16.7.1PyropeMg3Al2(SiO4)3Iso.
16.7.2SapphirineMg4(Mg3Al9)O4[Si3Al9O36]Mon. 2/m : P21/b
16.7.3Sapphirine-1A(Mg,Al,Fe2+)8[(Al,Si,Fe3+)6O18]O2Tric. 1 : P1
16.7.4MagnesiochloritoidMgAl2(SiO4)O(OH)2Mon. 2/m : B2/b
16.7.5KulkeiteMg8Al(AlSi7O20)(OH)10Mon.
16.7.6Palygorskite(Mg,Al)5(Si,Al)8O20(OH)2 · 8H2OMon. 2/m : B2/m
16.7.7SaponiteCa0.25(Mg,Fe)3((Si,Al)4O10)(OH)2 · nH2OMon.
16.7.8AliettiteCa0.2Mg6((Si,Al)8O20)(OH)4 · 4H2OMon.
16.7.10Baumite(Mg,Al,Mn,Zn,Fe)3(Si,Al)2O5(OH)4

Fluorescence of MontmorilloniteHide

Usually not fluorescent, except by mixtures with autunite, etc.

Other InformationHide

Thermal Behaviour:
Basal spacings collapse to lower values with dehydration
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Montmorillonite in petrologyHide

References for MontmorilloniteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Grim, R.E., Kulbicki, G. (1961) Montmorillonite: high-temperature reactions and classification. American Mineralogist: 46: 1329-1369.
Tettenhorst, R., Johns, W.D. (1966) Interstratification in montmorillonite. Clays and Clay Minerals: 25: 85-93.
McAtee, J.L., Henslee, W. (1969) Electron microscopy of montmorillonite dispersed at various pH. American Mineralogist: 54: 869-874.
Shutov, V.D., Drits, V.A., Sakharov, B.A. (1969) On the mechanism of a postsedimentary transformation of montmorillonite into hydromica. In L. Heller, Ed., Proceedings International Clay Conference, Tokyo, 1969, 1: 523-532, Jerusalem University.
Shutov, V.D., Drits, V.A., Sakharov, B.A. (1969) On the mechanism of a postsedimentary transformation of montmorillonite into hydromica: Discussion. In L. Heller, Ed., Proceedings International Clay Conference, Tokyo, 1969, 2: 126-129, Jerusalem University.
Tettenhorst, R., Roberson, H.E. (1973) X-ray diffraction aspects of montmorillonite. American Mineralogist: 58: 73-80.
Gillespie, J.B., Lindberg, J.D., Smith, M.S. (1974) Visible and near-infrared absorption coefficients of montmorillonite and related clays. American Mineralogist: 59: 1113-1116.
Lagaly, G., Fernandez-Gonzalez, M., Weiss, A. (1976) Problems in layer-charge determination of montmorillonites. Clay Minerals: 11: 173-187.
Sherman, D.M., Vergo, N. (1988) Optical spectrum, site occupancy, and oxidation state of Mn in montmorillonite. American Mineralogist: 73: 140-144.
Van Groos, A.F.K., Guggenheim, S. (1989) Dehydroxylation of Ca- and Mg-exchanged montmorillonite. American Mineralogist: 74: 627.
Muller, F., Besson, G., Manceau, A., Drits, V.A. (1997), Distribution of isomorphous cations within octahedral sheets in montmorillonite from Camp-Bertaux. Physica and Chemistry of Minerals: 24: 159-166.
Burford, E.P., Kierans, M., Gadd, G.M. (2003): Geomycology: fungi in mineral substrata. Mycologist: 17(3): 98-107; DOI: 10.1017/S0269915X03003112
Christidis, G.E. (2006) Genesis and compositional heterogeneity of smectites. Part III: Alteration of basic pyroclastic rocks - A case study from the Troodos Ophiolite Complex, Cyprus. American Mineralogist: 91: 685-701.

Internet Links for MontmorilloniteHide

Localities for MontmorilloniteHide

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.

Locality ListShow