Mineral phase
IMA name
Montmorillonite
Type
Class
silicate mineral
Compound type
phyllosilicate
Comments
Montmorillonite has a typical hydration number of 10
Chemical composition
Formula
$(Na,Ca)_{0.3}(Al,Mg)_2.Si_4O_{10}(OH)_2 \bullet n(H_2O)$
Chemical formula
(Na,Ca)0.3(Al,Mg)2Si4O10(OH)2•n(H2O)
Elemental formula
(Na)0-0.3 (Ca)0-0.3 (Al)1.65-2 (Mg)0-2 Si4 O12 H2
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Na$ Sodium element 0 - 0.3 constituent element main
$Ca$ Calcium element 0 - 0.3 constituent element main
$Al$ Aluminium element 1.65 - 2 constituent element main
$Mg$ Magnesium element 0 - 2 constituent element main
$Si$ Silicon element 4 constituent element main
$O$ Oxygen element 12 constituent element main
$H$ Hydrogen element 2 constituent element main
Composition comments
Typical formula: $(Na_{0.2}Ca_{0.1})Al_2.Si_4O_{10}(OH)_2 \bullet (H_2O)_{10}$ - Common impurities: Fe, K
Chemical functions
  Function Number
$(OH)^-$ 2
Chemical bonds
  Bond Number
$O^--H$ 1
Oxides
Formula $Na_{2}O$ $CaO$ $Al_{2}O_{3}$ $MgO$ $SiO_{2}$ $H_{2}O$
Mass fraction (%)

Strunz

Class
silicates (09)
Division
phyllosilicate (09.E)
Family
with mica sheets, composed of tetrahedral and octahedral nets (09.EC)
Code
09.EC.40

Dana

Major class
silicates (VIII)
Class
phyllosilicate sheets of six-membered rings (71)
Type
with 2:1 clays (71.03)
Group
Smectite group (Dioctahedral Smectites) (71.03.01a)
Code
71.03.01a.02
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
C2/m
Molar mass
549.07 $g/mol$
Density
2 - 2.7 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.015 - 0.020
Refraction index $n_{\alpha}$
1.485 - 1.535
Refraction index $n_{\beta}$
1.504 - 1.550
Refraction index $n_{\gamma}$
1.505 - 1.550
Dispersion V
0
Pure color
white
Color
gray white, yellow, brownish yellow, greenish yellow
Diaphaneity
translucent to opaque
Luster
earthy
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