Constituent
Name
Ca-exchanged smectite SWa-1 size-fraction <1 µm
IMA name
Montmorillonite
Class
silicate mineral
Compound type
phyllosilicate
Comments
Montmorillonite has a typical hydration number of 10 - Chemical composition and molecular mass are per half unit cell
Chemical composition
Formula
$Ca_{0.16}(Al_{0.67}Mg_{0.07}Fe_{1.26})(Si_{3.76}Al_{0.24})O_{10}(OH)_2$
Chemical formula
(Na,Ca)0.3(Al,Mg)2Si4O10(OH)2•n(H2O)
Elemental formula
(Ca)0.16-0.3 (Al)1.45-2 (Mg)0.49-2 Fe0.08 (Si)3.98-4 O12 H2
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Ca$ Calcium element 0.16 - 0.3 1.0 constituent element main
$Al$ Aluminium element 1.45 - 2 1.0 constituent element main
$Mg$ Magnesium element 0.49 - 2 1.0 constituent element main
$Fe$ Iron element 0.08 1.0 constituent element main
$Si$ Silicon element 3.98 - 4 1.0 constituent element main
$O$ Oxygen element 12 1.0 constituent element main
$H$ Hydrogen element 2 1.0 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 - Intermolecular water was not taken into account in atomic composition calculation
Chemical functions
  Function Number
$(OH)^-$ 2
Chemical bonds
  Bond Number
$O^--H$ 1
Oxides
Formula $SiO_{2}$ $Al_{2}O_{3}$ $MgO$ $Fe_{2}O_{3}$ $CaO$ $H_{2}O$
Mass fraction (%) 56.14 11.53 0.7 25.0 2.16 4.48

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
Texture
cryptocrystalline
Molar mass
402.0 $g/mol$
Density
N/A $g/cm^3$
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
Color
gray white, yellow, brownish yellow, greenish yellow
Diaphaneity
translucent to opaque
Luster
N/A