Montmorillonite Mineral Data

Montmorillonite Mineral Data +

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General Montmorillonite Information

Chemical Formula:

(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2·n(H2O)

Composition:

Molecular Weight = 549.07 gm

Sodium 0.84 % Na 1.13 % Na₂O

Calcium 0.73 % Ca 1.02 % CaO

Aluminum 9.83 % Al 18.57 % Al₂O₃

Silicon 20.46 % Si 43.77 % SiO₂

Hydrogen 4.04 % H 36.09 % H₂O

Oxygen 64.11 % O

______ ______

100.00 % 100.58 % = TOTAL OXIDE

Empirical Formula:

Na_0.2Ca_0.1Al₂Si₄O₁₀(OH)₂(H₂O)₁₀

IMA Status:

Valid Species (Pre-IMA) 1847

Locality:

Veinne, Montmorillone, France. Link to MinDat.org Location Data.

Name Origin:

Named after the locality.

Synonym:

Bentonite

Montmorillonite Image

Images:

Montmorillonite

Comments: Authigenic smectite (montmorillonite) overgrown on pore spaces and authigenicly-overgrown quartz grains in a sandstone. SEM image of a core sample.
Location: Unknown. Scale: Picture size 67 µ-m.
© OMNI Laboratories, Inc

Images:

Montmorillonite

Comments: Bright pink chalky massive montmorillonite.
Location: Tamminen Quarry, Greenwood, Oxford County, Maine, USA. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Montmorillonite Crystallography

Axial Ratios:

a:b:c =0.5782:1:1.1129

Cell Dimensions:

a = 5.17, b = 8.94, c = 9.95, Z = 1; beta = 99.9° V = 453.04 Den(Calc)= 2.01

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: C 2/m

Crystal Structure:

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Viani A , Gualtieri A , Artioli G , American Mineralogist , 87 (2002) p.966-975, The nature of disorder in montmorillonite by simulation of X-ray powder patterns, Note: Structural simulation model

Physical Properties of Montmorillonite

Cleavage:

[001] Perfect

Color:

White, Gray white, Yellow, Brownish yellow, Greenish yellow.

Density:

2 - 2.7, Average = 2.35

Diaphaniety:

Translucent to Opaque

Fracture:

Earthy - Dull, clay-like fractures with no visible crystalline affinities, (e.g. howlite).

Habit:

Earthy - Dull, clay-like texture with no visible crystalline affinities, (e.g. howlite).

Hardness:

1.5-2 - Talc-Gypsum

Luminescence:

None.

Luster:

Earthy (Dull)

Streak:

white

Optical Properties of Montmorillonite

Gladstone-Dale:

CI meas= 0.135 (Poor) - where the CI = (1-KPDmeas/KC)
CI calc= -0.012 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2595,KPDmeas= 0.2219,KC= 0.2565

Optical Data:

Biaxial (-), a=1.485-1.535, b=1.504-1.55, g=1.505-1.55, bire=0.0150-0.0200, 2V(Calc)=0-24, 2V(Meas)=5-30. Dispersion none.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Montmorillonite

Electron Density:

r_electron=2.08 gm/cc
note: r_{Montmorillonite}=2.01 gm/cc.

Fermion Index

Fermion Index = 0.00987
Boson Index = 0.99013

Photoelectric:

PE_{Montmorillonite}= 1.26 barns/electron
U=PE_{Montmorillonite} x r_electron= 2.63 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Montmorillonite is Not Radioactive

Montmorillonite Classification

Dana Class:

71.3.1a.2 (71)Phyllosilicate Sheets of Six-Membered Rings

(71.3)with 2:1 clays

(71.3.1a)Smectite group (Dioctahedral Smectites)

71.3.1a.1 Beidellite Na0.5Al2(Si3.5Al0.5)O10(OH)2·n(H2O) C 2/m or ORTH 2/m

71.3.1a.2 Montmorillonite (Na,Ca)0,3(Al,Mg)2Si4O10(OH)2·n(H2O) C 2/m 2/m

71.3.1a.3 Nontronite Na0.3Fe2(Si,Al)4O10(OH)2·n(H2O) C 2/m 2/m

71.3.1a.4 Volkonskoite Ca0.3(Cr,Mg,Fe)2(Si,Al)4O10(OH)2·4(H2O) C 2/m 2/m

71.3.1a.5 Swinefordite (Li,Ca0.5,Na)0.72(Li,Al,Mg)2.66(Si,Al)4O10(OH,F)2·2(H2O) C 2/m (MON or ORTH) 2/m

Strunz Class:

VIII/H.19-20 VIII - Silicates

VIII/H - Phyllosilicates (layered) Mica like with [Si4O10]4- and related groups

VIII/H.19 - Brammallite ? - Yakhontovite series

VIII/H.19-10 Brammallite* (Na,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)] C 2/c 2/m

VIII/H.19-10a Brinrobertsite! (Na,K,Ca)x(Al,Fe,Mg)4(Si,Al)8O20(OH)4·3.54(H2O)[x=0.35,n=3.54] pseudo 2/m 2/m

VIII/H.19-15 Illite* (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)] C 2/m 2/m

VIII/H.19-20 Montmorillonite (Na,Ca)0,3(Al,Mg)2Si4O10(OH)2·n(H2O) C 2/m 2/m

VIII/H.19-30 Beidellite Na0.5Al2(Si3.5Al0.5)O10(OH)2·n(H2O) C 2/m or ORTH 2/m

VIII/H.19-40 Nontronite Na0.3Fe2(Si,Al)4O10(OH)2·n(H2O) C 2/m 2/m

VIII/H.19-50 Volkonskoite Ca0.3(Cr,Mg,Fe)2(Si,Al)4O10(OH)2·4(H2O) C 2/m 2/m

VIII/H.19-60 Swinefordite (Li,Ca0.5,Na)0.72(Li,Al,Mg)2.66(Si,Al)4O10(OH,F)2·2(H2O) C 2/m (MON or ORTH) 2/m

VIII/H.19-70 Yakhontovite (Ca,K)0.5(Cu,Fe,Mg)2Si4O10(OH)2·3(H2O) C 2/m 2/m

Other Montmorillonite Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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Montmorillonite

(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2·n(H2O)
Dana No: 71.3.1a.2 Strunz No: VIII/H.19-20
Locality:

Notes: