University of Colorado

Mineral Structure Data

Amphibole Group

The amphibole group is composed of minerals of the general formula

The crystal structure of amphibole.


Orthoamphibole Unit Cells


End-Member           Anthophyllite              Gedrite


Formula        (Mg5.53Fe1.47)(Na.5Ca.03)Si8O22(OH)2        (Fe 1.1Mg4.5Al1.2) (Al1.8Si6.3)O22(OH,F)2


Form.Wt. 827.23 827.42 Density 3.111 3.184 Mol Volume 265.88 259.84 Z 4 4 Cryst.Sys. Orthorhombic Orthorhombic Cryst.Class mmm mmm Space Group Pnma Pnma Cell Parameters a(Å) 18.560 18.531 b(Å) 18.013 17.741 c(Å) 5.2818 5.249 Vol. 1765.82 1725.65 Reference Finger Papike & (1970) Ross (1970) Thermal Expansion(Volumetric) alpha a0 a1 a2 Elastic Properties Ks(GPa) G(Gpa)

Ortho-amphibole Octahedral Sites.


End-Member                       Anthophyllite                                             Gedrite

Site            M1           M2           M3           M4              M1           M2           M3           M4
C.N.            6            6            6            7               6            6            6            6
Occupant        Mg.96Fe.04     Mg.9 7Fe.03    Mg.97Fe.03     Mg.35Fe.65        Mg.88Fe.12    Mg.4Al.6    Mg .9Fe.1    Mg.55Fe.45

Point Sym.      1            1            m            1               1            1            m            1
Wyckoff Not.    8d           8d           4c           8d              8d           8d           4c           8d

Frac.Coord.
x              .12489        .12488       .12579       .12371          .1244        .1248        .1249        .1189
y              .16329        .07317        1/4        -.00982          .1611        .0731        1/4         -.0145
z              .3911        -.1099        -.1089        .3877          .3737        -.1281        -.1248      .3636

Distances
Mean           2.084         2.076         2.070       2.349           2.093        1.987        2.059        2.185
sigma           .032          .049          .011        .374            .042         .042         .035         .138

Poly.Vol.      11.877        11.765        11.595      17.281          11.923       10.379       11.274       12.766
Q.E.           1.0107        1.0094        1.0138        --            1.0171       1.0058       1.0222       1.0622
Ang.Var.       34.7          30.8          44.8          --            54.3         18.6         70.8         202.3

Site Energy    -1053.        -1201.        -1044.      -1071.          -1027.       -1906.       -1054.       -1059.
Model Charge   2.0           2.0           2.0         2.0             2.0          2.6          2.0          2.0


Ortho-amphibole Tetrahedral Sites.



End-Member                        Anthophyllite                                Gedrite

Site            T1A        T1B        T2A        T2B              T1A        T1B        T2A        T2B
C.N.            4          4          4          4                4          4          4          4
Occupant        Si         Si         Si         Si               Si.66Al.34    Si.62Al.38   Si        Si.84Al.16

Point Sym.      1          1          1          1                1          1          1          1
Wyckoff Not.    8d         8d         8d         8d               8d         8d         8d         8d

Frac.Coord.
x               .23039     .01863     .22731     .02469           .2315      .0202      .2278      .0266
y              -.1654     -.16626    -.07956    -.08177          -.1631     -.1645     -.0760     -.0802
z              -.4334      .2760      .0622     -.2227           -.4487      .2971      .0502     -.1985

Distances
Mean           1.620      1.622      1.624      1.633            1.650      1.656      1.616      1.649
sigma           .013       .011       .023       .020             .017       .009       .026       .017

Poly.Vol.      2.183      2.189      2.175      2.221            2.306      2.331      2.140      2.286
Q.E.           1.0002     1.0001     1.0076     1.0046           1.0006     1.0001     1.0087     1.0041
Ang.Var.       0.9        0.3        30.5       18.4             2.3        0.7        33.4       15.5

Site Energy    -4433.     -4403.     -4425.     -4393.           -3769.     -3701.     -4405.     -4062.
Model Charge   4.0        4.0        4.0        4.0              3.66        3.62       4.00       3.84



Mineral Data Base Index

GEOL 1010 Syllabus

GEOL 3010 Syllabus

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