Mineral phase
IMA name
Epidote
IMA Code
Ep
Type
Class
silicate mineral
Compound type
sorosilicate
Chemical composition
Formula
$Ca_2(Fe^{3+},Al)_3(SiO_4)_3(OH)$
Chemical formula
Ca2(Fe3+,Al)3(SiO4)3(OH)
Elemental formula
H (O-) (Ca2+)2 (Fe3+)0-3 (Al)0-3 Si3 O12
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$(OH)^-$ Hydroxide anion chemical function 1 anionic radical main
$Ca^{2+}$ Calcium cation element 2 constituent cation main
$Fe^{3+}$ Iron(III) cation element 0 - 3 constituent cation main
$Al$ Aluminium element 0 - 3 constituent element main
$Si$ Silicon element 3 constituent element main
$O$ Oxygen element 12 constituent element main
Oxides
Formula $CaO$ $Al_{2}O_{3}$ $Fe_{2}O_{3}$ $SiO_{2}$ $H_{2}O$
Mass fraction (%) 21.6 7.36 34.6 34.71 1.73

Strunz

Class
silicates (09)
Division
sorosilicate (09.B)
Family
with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination (09.BG)
Code
09.BG.05a

Dana

Major class
silicates (VIII)
Class
sorosilicate insular, mixed, single, and larger tetrahedral groups (58)
Type
with cations in [6] and higher coordination; single and double groups (n=1,2) (58.02)
Group
Epidote group (Clinozoisite subgroup) (58.02.01a)
Code
58.02.01a.02
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
P2(1)/m
Molar mass
519.30 $g/mol$
Density
3.3 - 3.6 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.0130 - 0.0460
Refraction index $n_{\alpha}$
1.723 - 1.751
Refraction index $n_{\beta}$
1.73 - 1.784
Refraction index $n_{\gamma}$
1.736 - 1.797
Dispersion V
strong, r > v
Color
yellowish green, brownish green, black, yellow, gray
Diaphaneity
transparent to opaque
Luster
vitreous
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