Mineral phase
IMA name
Fayalite
Type
Class
silicate mineral
Compound type
nesosilicate
Comments
Fayalite: name by extension of (Fe,Mg)2SiO4 in the range Mg=0-10% - Equivalent Space Group: Pbnm (62)
Chemical composition
Formula
$Fe^{2+}_2\!.SiO_4$
Chemical formula
(Fe2+)2SiO4
Elemental formula
(Fe2+)2 Si O4
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
$Si$ Silicon element 1 constituent element main
$O$ Oxygen element 4 constituent element main
Composition comments
Common substitution: Mg - Common impurities: Mn
Chemical functions
  Function Number
$(SiO_4)^{4-}$ 1
Chemical bonds
  Bond Number
$\geq Si-O^-$ 4
Oxides
Formula $FeO$ $SiO_{2}$
Mass fraction (%) 70.51 29.49

Strunz

Class
silicates (09)
Division
nesosilicate (09.A)
Family
without additional anions; cations in octahedral [6] coordination (09.AC)
Code
09.AC.05

Dana

Major class
silicates (VIII)
Class
nesosilicate insular SiO4 groups only (51)
Type
with all cations in octahedral [6] coordination (51.03)
Group
Olivine group (51.03.01)
Code
51.03.01.01
Phase type
crystalline
Crystal system
orthorhombic
Crystal class
dipyramidal
Crystal class symbol
mmm (D2h)
Crystal spacegroup
Pnma
Composition order
ordered
Molar mass
203.78 $g/mol$
Density
4.39 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.0420 - 0.0510
Refraction index $n_{\alpha}$
1.731 - 1.824
Refraction index $n_{\beta}$
1.76 - 1.864
Refraction index $n_{\gamma}$
1.773 - 1.875
Pure color
brown
Color
brown, black
Diaphaneity
transparent to translucent
Luster
vitreous
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