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Montmorillonite

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Formula:
(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O
System:
Monoclinic
Colour:
White, buff, yellow, ...
Hardness:
1 - 2
Member of:
Name:
For the type locality at Montmorillon, Vienne, Poitou-Charentes, France.
Isostructural with:

Classification of Montmorillonite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
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
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http://www.mindat.org/min-2821.html
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Type Occurrence of Montmorillonite

General Appearance of Type Material:
Compact earthy massive mineral.
Year of Discovery:
1847

Occurrences of Montmorillonite

Geological Setting:
Alteration product of volcanic tuffs and ash. Late-hydrothermal formation in various rocks.

Physical Properties of Montmorillonite

Dull, Earthy
Diaphaneity (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 (Mohs):
1 - 2
Comment:
Soft because of fine-grained occurrence
Cleavage:
Perfect
on {001}
Fracture:
Irregular/Uneven
Density:
2 - 3 g/cm3 (Measured)    

Crystallography of Montmorillonite

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

Optical Data of Montmorillonite

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 Montmorillonite

Formula:
(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O
Essential elements:
All elements listed in formula:
Common Impurities:
Fe,K

Relationship of Montmorillonite to other Species

Series:
Forms a series with Beidellite (see here)
Member of:
Other Members of Group:
AliettiteCa0.2Mg6((Si,Al)8O20)(OH)4 · 4H2O
Beidellite(Na,Ca0.5)0.3Al2((Si,Al)4O10)(OH)2 · nH2O
FerrosaponiteCa0.3(Fe2+,Mg,Fe3+)3((Si,Al)4O10)(OH)2 · 4H2O
HectoriteNa0.3(Mg,Li)3(Si4O10)(F,OH)2
NontroniteNa0.3Fe2((Si,Al)4O10)(OH)2 · nH2O
PimeliteNi3Si4O10(OH)2·4H2O
Saliotite(Li,Na)Al3(AlSi3O10)(OH)5
SaponiteCa0.25(Mg,Fe)3((Si,Al)4O10)(OH)2 · nH2O
SauconiteNa0.3Zn3((Si,Al)4O10)(OH)2 · 4H2O
Stevensite(Ca,Na)xMg3-x(Si4O10)(OH)2
SwineforditeLi(Al,Li,Mg)4((Si,Al)4O10)2(OH,F)4 · nH2O
VolkonskoiteCa0.3(Cr,Mg,Fe)2((Si,Al)4O10)(OH)2 · 4H2O
Yakhontovite(Ca,Na)0.5(Cu,Fe,Mg)2(Si4O10)(OH)2 · 3H2O
ZincsiliteZn3(Si4O10)(OH)2 · 4H2O
Structurally related to group(s):
9.EC.05Minnesotaite(Fe,Mg)3(Si4O10)(OH)2
9.EC.05TalcMg3(Si4O10)(OH)2
9.EC.05Willemseite(Ni,Mg)3(Si4O10)(OH)2
9.EC.10FerripyrophylliteFe23+(Si4O10)(OH)2
9.EC.10PyrophylliteAl2(Si4O10)(OH)2
9.EC.15BoromuscoviteKAl2(BSi3O10)(OH)2
9.EC.15CeladoniteK(Mg,Fe2+)Fe3+(Si4O10)(OH)2
9.EC.15Chernykhite(Ba,Na)(V3+,Al,Mg)2((Si,Al)4O10)(OH)2
9.EC.15Montdorite(K,Na)2(Fe2+,Mn2+,Mg)5(Si4O10)2(OH,F)4
9.EC.15MuscoviteKAl2(AlSi3O10)(OH)2
9.EC.15NanpingiteCsAl2(AlSi3O10)(OH,F)2
9.EC.15ParagoniteNaAl2(AlSi3O10)(OH)2
9.EC.15RoscoeliteK(V3+,Al)2(AlSi3O10)(OH)2
9.EC.15Tobelite(NH4,K)Al2(AlSi3O10)(OH)2
9.EC.15AluminoceladoniteK(Mg,Fe2+)Al(Si4O10)(OH)2
9.EC.15ChromphylliteK(Cr,Al)2(AlSi3O10)(OH,F)2
9.EC.15FerroaluminoceladoniteK(Fe2+,Mg)(Al,Fe3+)(Si4O10)(OH)2
9.EC.15FerroceladoniteK(Fe2+,Mg)(Fe3+,Al)(Si4O10)(OH)2
9.EC.15ChromceladoniteK(Mg,Fe2+)(Cr,Al)(Si4O10)(OH)2
9.EC.15TainioliteKLiMg2(Si4O10)F2
9.EC.15Ganterite(Ba,Na,K)(Al,Mg)2(AlSi3O10)(OH)2
9.EC.20AnniteKFe32+(AlSi3O10)(OH)2
9.EC.20EphesiteLiNaAl2(Al2Si2O10)(OH)2
9.EC.20HendricksiteK(Zn,Mg,Mn2+)3(AlSi3O10)(OH)2
9.EC.20Masutomilite(K,Rb)(Li,Mn3+,Al)3(AlSi3O10)(F,OH)2
9.EC.20NorrishiteKLiMn23+(Si4O10)O2
9.EC.20PhlogopiteKMg3(AlSi3O10)(OH)2
9.EC.20PolylithioniteKLi2Al(Si4O10)(F,OH)2
9.EC.20PreiswerkiteNaMg2Al(Al2Si2O10)(OH)2
9.EC.20SiderophylliteKFe22+Al(Al2Si2O10)(OH)2
9.EC.20TetraferriphlogopiteKMg3(Fe3+Si3O10)(OH,F)2
9.EC.20FluorotetraferriphlogopiteKMg3(Fe3+Si3O10)F2
9.EC.20Wonesite(Na,K)(Mg,Fe,Al)6((Al,Si)4O10)2(OH,F)4
9.EC.20EastoniteKMg2Al(Al2Si2O10)(OH)2
9.EC.20TetraferrianniteKFe32+((Fe3+,Al)Si3O10)(OH)2
9.EC.20TrilithioniteK(Li1.5Al1.5)(AlSi3O10)(F,OH)2
9.EC.20FluoranniteKFe32+(AlSi3O10)(F,OH)2
9.EC.20ShirokshiniteKNaMg2(Si4O10)F2
9.EC.20ShirozuliteK(Mn2+,Mg)3(AlSi3O10)(OH)2
9.EC.20SokolovaiteCsLi2Al(Si4O10)F2
9.EC.20AspidoliteNaMg3(AlSi3O10)(OH)2
9.EC.20FluorophlogopiteKMg3(AlSi3O10)(F,OH)2
9.EC.20UM2004-49-SiO:AlCsFHKLi(Cs,K)(Al,Li)2.6((Si,Al)4O10)(F,OH)2
9.EC.20Suhailite(NH4)Fe32+(AlSi3O10)(OH)2
9.EC.20YangzhumingiteKMg2.5(Si4O10)F2
9.EC.20OrloviteKLi2Ti(Si4O10)OF
9.EC.20OxyphlogopiteK(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2
9.EC.25Brammallite(Na,H3O)(Al,Mg,Fe)2((Si,Al)4O10)(OH)2
9.EC.30MargariteCaAl2(Al2Si2O10)(OH)2
9.EC.35Anandite(Ba,K)(Fe2+,Mg)3((Si,Al,Fe)4O10)(S,OH)2
9.EC.35BityiteLiCaAl2(AlBeSi2O10)(OH)2
9.EC.35ClintoniteCa(Mg,Al)3(Al3SiO10)(OH)2
9.EC.35Kinoshitalite(Ba,K)(Mg,Mn2+,Al)3(Al2Si2O10)(OH)2
9.EC.35Ferrokinoshitalite(Ba,K)(Fe2+,Mg)3(Al2Si2O10)(OH,F)2
9.EC.35Oxykinoshitalite(Ba,K)(Mg,Ti,Fe3+,Fe2+)3((Si,Al)4O10)(O,OH,F)2
9.EC.35FluorokinoshitaliteBaMg3(Al2Si2O10)F2
9.EC.40Beidellite(Na,Ca0.5)0.3Al2((Si,Al)4O10)(OH)2 · nH2O
9.EC.40Kurumsakite(Zn,Ni,Cu)8Al8V25+Si5O35 · 27H2O (?)
9.EC.40NontroniteNa0.3Fe2((Si,Al)4O10)(OH)2 · nH2O
9.EC.40VolkonskoiteCa0.3(Cr,Mg,Fe)2((Si,Al)4O10)(OH)2 · 4H2O
9.EC.40Yakhontovite(Ca,Na)0.5(Cu,Fe,Mg)2(Si4O10)(OH)2 · 3H2O
9.EC.45HectoriteNa0.3(Mg,Li)3(Si4O10)(F,OH)2
9.EC.45SaponiteCa0.25(Mg,Fe)3((Si,Al)4O10)(OH)2 · nH2O
9.EC.45SauconiteNa0.3Zn3((Si,Al)4O10)(OH)2 · 4H2O
9.EC.45SpadaiteMgSiO2(OH)2 · H2O (?)
9.EC.45Stevensite(Ca,Na)xMg3-x(Si4O10)(OH)2
9.EC.45SwineforditeLi(Al,Li,Mg)4((Si,Al)4O10)2(OH,F)4 · nH2O
9.EC.45ZincsiliteZn3(Si4O10)(OH)2 · 4H2O
9.EC.45FerrosaponiteCa0.3(Fe2+,Mg,Fe3+)3((Si,Al)4O10)(OH)2 · 4H2O
9.EC.50Vermiculite(Mg,Fe,Al)3((Al,Si)4O10)(OH)2 · 4H2O
9.EC.55Baileychlore(Zn,Fe,Al,Mg)6((Si,Al)4O10)(OH)8
9.EC.55Chamosite(Fe2+,Mg)5Al(AlSi3O10)(OH)8
9.EC.55Clinochlore(Mg,Fe2+)5Al(AlSi3O10)(OH)8
9.EC.55Cookeite(Al2Li)Al2(AlSi3O10)(OH)8
9.EC.55FranklinfurnaceiteCa2Fe3+Mn32+Mn3+(Zn2Si2O10)(OH)8
9.EC.55Gonyerite(Mn2+,Mg)5Fe3+(Fe3+Si3O10)(OH)8
9.EC.55Nimite(Ni,Mg,Al)6((Si,Al)4O10)(OH)8
9.EC.55Orthochamosite(Fe2+,Mg,Fe3+)5Al(AlSi3O10)(OH,O)8
9.EC.55PennantiteMn52+Al(AlSi3O10)(OH)8
9.EC.55Sudoite(Mg,Fe2+)2Al3(AlSi3O10)(OH)8
9.EC.55DonbassiteAl4.33(AlSi3O10)(OH)8
9.EC.55GlagoleviteNa(Mg,Al)6(AlSi3O10)(OH,O)8
9.EC.55BorocookeiteLi1+3xAl4-x(BSi3O10)(OH)8
9.EC.60AliettiteCa0.2Mg6((Si,Al)8O20)(OH)4 · 4H2O
9.EC.60Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
9.EC.60DozyiteMg7Al2(Al2Si4O15)(OH)12
9.EC.60HydrobiotiteK(Mg,Fe2+)6((Si,Al)8O20)(OH)4 · nH2O
9.EC.60Karpinskite(Ni,Mg)2Si2O5(OH)2 (?)
9.EC.60KulkeiteMg8Al(AlSi7O20)(OH)10
9.EC.60LunijianlaiteLi0.7Al6.2(AlSi7O20)(OH,O)10
9.EC.60Rectorite(Na,Ca)Al4((Si,Al)8O20)(OH)4 · 2H2O
9.EC.60Saliotite(Li,Na)Al3(AlSi3O10)(OH)5
9.EC.60TosuditeNa0.5(Al,Mg)6((Si,Al)8O18)(OH)12 · 5H2O
9.EC.60BrinrobertsiteNa0.3Al4(Si4O10)2(OH)4 · 3.5 H2O
9.EC.65Macaulayite(Fe,Al)24Si4O43(OH)2
9.EC.70BurckhardtitePb2(Fe3+Te6+)[AlSi3O8]O6
9.EC.75Ferrisurite(Pb,Ca)2.4Fe23+(Si4O10)(CO3)1.7(OH)3 · nH2O
9.EC.75Surite(Pb,Ca)3(Al,Fe2+,Mg)2((Si,Al)4O10)(CO3)2(OH)2
9.EC.75Niksergievite(Ba,Ca)2Al3(AlSi3O10)(CO3)(OH)6 · nH2O
9.EC.80KegelitePb8Al4(Si8O20)(SO4)2(CO3)4(OH)8
16.7.1PyropeMg3Al2(SiO4)3
16.7.2Sapphirine(Mg,Fe)4-xAl4+x[Al4+xSi2-xO18]O2
16.7.3Sapphirine-1A(Mg,Al,Fe2+)8[(Al,Si,Fe3+)6O18]O2
16.7.4MagnesiochloritoidMgAl2(SiO4)O(OH)2
16.7.5KulkeiteMg8Al(AlSi7O20)(OH)10
16.7.6Palygorskite(Mg,Al)5(Si,Al)8O20(OH)2 · 8H2O
16.7.7SaponiteCa0.25(Mg,Fe)3((Si,Al)4O10)(OH)2 · nH2O
16.7.8AliettiteCa0.2Mg6((Si,Al)8O20)(OH)4 · 4H2O
16.7.10Baumite(Mg,Al,Mn,Zn,Fe)3(Si,Al)2O5(OH)4

Other Names for Montmorillonite

Other Information

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

References for Montmorillonite

Reference List:
Grim, Ralph Early & G. Kulbicki (1961), Montmorillonite: high-temperature reactions and classification: American Mineralogist: 46: 1329-1369.

Tettenhorst, R. and W.D. Johns (1966), Interstratification in montmorillonite: Clays and Clay Minerals: 25: 85-93.

McAtee, J.L. & W. Henslee (1969), Electron microscopy of montmorillonite dispersed at various pH: American Mineralogist: 54: 869-874.

Shutov, V.D., V.A. Drits, and B.A. Sakharov (1969a), 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., V.A. Drits, and B.A. Sakharov (1969b), 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. and Roberson, H.E. (1973) X-ray diffraction aspects of montmorillonite. American Mineralogist: 58: 73-80.

Gillespie, J. B., J.D. Lindberg & M.S. Smith (1974), Visible and near-infrared absorption coefficients of montmorillonite and related clays: American Mineralogist: 59: 1113-1116.

Lagaly, G., M. Fernandez-Gonzalez, and A. Weiss (1976), Problems in layer-charge determination of montmorillonites: Clay Minerals: 11: 173-187.

Sherman, D.M. and N. Vergo (1988), Optical spectrum, site occupancy, and oxidation state of Mn in montmorillonite: American Mineralogist: 73: 140-144.

American Mineralogist (1989): 74: 627.

Muller, F., G. Besson, A. Manceau, and V.A. Drits (1997), Distribution of isomorphous cations within octahedral sheets in montmorillonite from Camp-Bertaux: Physica and Chemistry of Minerals: 24: 159-166.

Christidis, George 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 Montmorillonite

Specimens:
The following Montmorillonite specimens are currently listed for sale on minfind.com.

Localities for Montmorillonite

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.
Mineral and/or Locality  
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