Mineral phase
IMA name
Cronstedtite
Type
Class
silicate mineral
Compound type
phyllosilicate
Chemical composition
Formula
$Fe^{2+}_2Fe^{3+}.(SiFe^{3+})O_5(OH)_4$
Chemical formula
(Fe2+)2(Fe3+)(SiFe3+)O5(OH)4
Elemental formula
(Fe2+)2 (Fe3+)2 Si O9 H4
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Fe^{2+}$ Iron(II) cation element 2 constituent element main
$Fe^{3+}$ Iron(III) cation element 2 constituent element main
$Si$ Silicon element 1 constituent element main
$O$ Oxygen element 9 constituent element main
$H$ Hydrogen element 4 constituent element main
Composition comments
Common impurities: Al, Ca
Chemical functions
  Function Number
$(OH)^-$ 4
Chemical bonds
  Bond Number
$O^--H$ 1
Oxides
Formula $FeO$ $Fe_{2}O_{3}$ $SiO_{2}$ $H_{2}O$
Mass fraction (%) 35.97 39.97 15.04 9.02

Strunz

Class
silicates (09)
Division
phyllosilicate (09.E)
Family
Phyllosilicates with kaolinite layers (09.ED)
Code
09.ED.15

Dana

Major class
silicates (VIII)
Class
phyllosilicate sheets of six-membered rings (71)
Type
with 1:1 layers (71.01)
Group
Serpentine group (Amesite subgroup) (71.01.02c)
Code
71.01.02c.07
Phase type
crystalline
Crystal system
trigonal
Crystal class
ditrigonal-pyramidal
Crystal class symbol
3m (C3v)
Crystal spacegroup
P31m
Molar mass
399.50 $g/mol$
Density
3.34 - 3.35 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.080
Refraction index $n_{\alpha}$
1.72
Refraction index $n_{\beta}$
1.8
Refraction index $n_{\gamma}$
1.8
Dispersion V
moderate, r < v
Pure color
black
Color
black, greenish black, brownish black, dark brown
Diaphaneity
transparent to translucent
Luster
vitreous
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