Geoscience Reference
In-Depth Information
Table 5.1
Adsorption data of N
2
on goethite. Pressures
refer to the nitrogen gas
P
(10
−
12
Pa)
V
(10
−
6
m
3
g
−
1
)
251
8.5
176
7.9
128
7.2
97
6.6
70
6.0
45
4.9
30
3.9
20.7
3.1
and groundwater. How far will groundwater movement take a contamination in 10 000
years for the following elements: Cl (
D
Cl
0), I (
D
I
0.01), Sr (
D
Sr
=
=
=
0.2), U
10
8
)?
12. Basaltic melt percolates through a matrix of molten peridotite. Let us assume that the
degree of melting (
F
(
D
Yb
100), Th (
D
Th
=
=
2 percent) does not change significantly over the distance of
interest. Discuss the relative velocity of Ni (
D
Ni
=
10), Yb (
D
Yb
1), and Ba (
D
Ba
=
0.0001). Compare the velocity of incompatible elements (e.g. Ba) and major elements
(e.g. Si, Al) and discuss which core assumption of the chromatography theory breaks
down for the latter group.
13. Calculate the surface area in m
2
g
−
1
of goethite, FeO(OH), at ambient temperature
using the volumes
V
of N
2
(in m
3
g
−
1
) adsorbed under the pressures
P
of this gas as
listed in
Table 5.1
. Use a Langmuir isotherm and a cross-section of 1.64
=
=
10
−
18
m
2
for the N
2
molecule. One mole of gas under standard conditions is 0.0224 m
3
. Assume
that the shape of the crystals is roughly spherical. The specific gravity of goethite is
3.6gcm
−
3
and the mean diameter of mineral grains is 100
×
m. Compare the actual
surface area of 1 g of powder with the surface area derived from the adsorption data.
μ
References
Cherniak, D. J., Lanford, W. A., and Ryerson, F. J. (2001) Lead diffusion in apatite
and zircon using ion implantation and Rutherford backscattering techniques.
Geochim.
Cosmochim. Acta
,
55
, 1663-1673.
Cygan, R. T. and Lasaga, A. C. (1985) Self-diffusion of magnesium in garnet at 750
◦
to
900
◦
C.
Amer. J. Sci.
,
285
, 328-350.
♠
Dodson, M. H. (1973) Closure temperature in cooling geochronological and petrological
systems.
Contrib. Mineral. Petrol.
,
40
, 259-274.
♠
DeVault, D. (1943) The theory of chromatography.
J. Amer. Chem. Soc.
,
65
, 532-540.
