Mineral phase
IMA name
Chamosite
Type
Class
silicate mineral
Compound type
phyllosilicate
Chemical composition
Formula
$(Mg,Fe^{2+},Fe^{3+})_5Al(Si_3Al)O_{10}(OH,O)_8$
Chemical formula
(Mg,Fe2+,Fe3+)5Al(Si3Al)O10(OH,O)8
Elemental formula
(Mg)0-2 (Fe2+)2-4 (Fe3+)0-1 Al2 Si3 O18 (H)6-8
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Mg$ Magnesium element 0 - 2 constituent element main
$Fe^{2+}$ Iron(II) cation element 2 - 4 constituent element main
$Fe^{3+}$ Iron(III) cation element 0 - 1 constituent element main
$Al$ Aluminium element 2 constituent element main
$Si$ Silicon element 3 constituent element main
$O$ Oxygen element 18 constituent element main
$H$ Hydrogen element 6 - 8 constituent element main
Composition comments
Fe3+ is minor or nonexistent. Common impurities: Ca, Na
Chemical functions
  Function Number
$(OH)^-$
Chemical bonds
  Bond Number
$O^--H$ 1
Oxides
Formula $MgO$ $Al_{2}O_{3}$ $FeO$ $Fe_{2}O_{3}$ $SiO_{2}$ $H_{2}O$
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.55

Dana

Major class
silicates (VIII)
Class
phyllosilicate sheets of six-membered rings (71)
Type
interlayered 1:1, 2:1, and octahedra (71.04)
Group
Chlorite group (Tri-Dioctahedral) (71.04.01)
Code
71.04.01.07
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
C2/m
Molar mass
664.18 $g/mol$
Density
3 - 3.4 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.0700
Refraction index $n_{\alpha}$
1.595 - 1.671
Refraction index $n_{\beta}$
1.599 - 1.684
Refraction index $n_{\gamma}$
1.599 - 1.685
Dispersion V
r < v weak
Pure color
green
Color
Green, Gray, Greenish gray, Brown, Blackish green, black
Diaphaneity
translucent to opaque
Luster
vitreous
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