University of Colorado
Mineral Structure Data
Hydroxide Group
The hydroxide group is composed of non-silicate minerals
withOH as the principal polyanionic species.
The crystal structure of diaspore.
The crystal structure of brucite.
End-Member Gibbsite Diaspore Boehmite Brucite Goethite
Formula Al(OH)3 AlO(OH) AlO(OH) Mg(OH)2 FeO(OH)
Form.Wt. 78.004 59.988 59.988 58.327 88.854
Density 2.421 3.377 3.075 2.377 4.294
Mol Volume 32.222 17.862 19.507 24.524 20.693
Z 8 4 4 1 4
Cryst.Sys. Monoclinic Orthorhombic Orthorhombic Trigonal Orthorhombic
Cryst.Class 2/m mmm mmm 3m1 mmm
Space Group P21/n Pbnm Amam P3m1 Pbnm
Cell Parameters
a(Å) 8.684 4.401 3.693 3.142 4.587
b(Å) 5.078 9.421 12.221 3.142 9.937
c(Å) 9.736 2.845 2.865 4.766 3.015
beta 94.54
Vol. 427.98 117.96 129.30. 40.75 137.43
Ref. Saalfeld & Busing & Hill Zigan & Forsyth
Wedde (1974) Levy (1958) (1981) Rothbauer(1967) et
al.(1968)
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Table 3.1.2. Hydroxide Cation Sites
End-Member Gibbsite Gibbsite Diaspore Boehmite Brucite Goethite
C.N. 6 6 6 6 6 6
Occupant Al(1) Al(2) Al Al Mg Fe
Point Sym. 1 1 m mm
3m m
Wyckoff Not. 4e 4e 4c 4c 1a 4c
Frac.Coord.
x 0.1679 0.3344 0.0451 0.25 0 0.0477
y 0.5259 0.0236 -0.1446 -0.3178 0 0.8539
z -0.0023 -0.0024 1/4 0 0 1/4
Distances
O1 1.910 1.930 (2) 1.851 (2) 1.944 (6) 2.099 (2)
1.957
(1) 1.858 (2) 1.878 (1) 1.926
(2) 1.893 (2) 2.095
O2 1.922 1.922 (2) 1.975
(1) 1.980
O3 1.925 1.881
O4 1.906 1.890
O5 1.832 1.862
O6 1.918 1.947
Mean 1.902 1.905 1.915 1.905 2.099 2.021
sigma .035 .033 .067 .031 .000 .082
Poly.Vol. 9.019 9.061 9.100 9.000 12.039 10.667
Q.E. 1.0120 1.0120 1.0205 1.0164 1.0161 1.0226
Ang.Var. 42.5 42.5 64.0 52.0 52.0 69.2
Site Energy -2408. -2396. -2484. -2204. -1139. -2352.
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