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
Phyllosilicates 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
Links