Mineral Structure Data
The olivine group is composed of minerals of the general formula
X2SiO4
where X = Mg ,Fe2+, or Ca; Y = Al, Cr, or Fe3+;
and Z = Si. The X-site is 8 coordinated, the Y -site is 6-coordinated
(octahedral) and the Z-site is 4-coordianted (tetrahedral).
The crystal structure of garnet showing its framework like structure of octahedra and tetrahedra. In the cubic structures, all oxygens are identical and are each bonded to one tetrahedron and one octahedron and to two of the divalent dodecahedral sites (circles). Oxygen lies in a general position (point symemtry 1), and there are 96 per unit cell.
Forsterite Fayalite Tephroite Liebenbergite Ca-olivine Co-olivine Monticellite Kirschsteinite
Form.Wt. 140.70 203.77 201.96 209.50 172.24 209.95 156.48 188.01
Z 4 4 4 4 4 4 4 4 4 4 4 4 4 4
CrystalSystem Orth Orth Orth Orth Orth Orth Orth Orth
PointGroup mmm mmm mmm mmm mmm mmm mmm mmm
SpaceGroup Pbnm Pbnm Pbnm Pbnm Pbnm Pbnm Pbnm Pbnm
UnitCell
a(Å) 4.7534 4.8195 4.9023 4.726 5.078 4.7811 4.822 4.844
b(Å) 10.1902 10.4788 10.5964 10.118 10.225 10.2998 11.108 10.577
c(Å) 5.9783 6.0873 6.2567 5.913 6.760 6.0004 6.382 6.146
Vol 289.58 307.42 325.02 282.75 385.32 295.49 341.84 314.89
MolarVol 43.603 46.290 48.939 42.574 58.020 44.493 51.472 47.415
Density 3.227 4.402 4.127 4.921 2.969 4.719 3.040 3.965
Thermal Expansion(Volumetric)
alpha 26.4 26.1 22.6 27.3 24.2
a0 0.3034 0.2386 0.2307 0.3036 0.3114
a1 0.7422 1.1530 1.0740 0.5598 0.6733
a2 -0.5381 -0.0518 -0.2898 -0.4204 -0.8133
Elastic Parameters
Ks(GPa) 129.5 134. 128. 165. 148. 106.
G(GPa) 81.1 50.7 54. 80.
|
|---|