Geoscience Reference
In-Depth Information
Table 1.3 Concentrations of transition elements of the first row in some glassy samples from the East Pacific
Rise (EPR) and also the mean value of these concentrations calculated in MORB from a much larger set of
samples. Data in ppm except for TiO 2 ,MnO,andFeO,whicharegiveninweight%
Sample
Sc
TiO 2
V
Cr nO
FeO
Co
Ni
Cu
Zn
1
26.6
2.07
176
5.99
0.22
11.8
26.8
10.6
45.9
131
2
41.0
2.27
385
23.4
0.22
12.7
46.3
33.5
74.9
114
3
44.1
3.21
361
81.7
0.25
15.3
45.8
72.7
74.3
115
4
43.6
1.77
308
161
0.21
10.8
45.8
64.4
86.8
92.4
5
38.1
2.08
277
204
0.17
10.2
45.4
104
72.7
88.2
6
32.4
0.96
180
383
0.13
8.5
45.3
145
93.4
50.5
7
33.7
1.34
207
665
0.17
9.2
52.7
632
81.2
68.4
Mean EPR
38.7
1.90
270
199
0.20
10.8
43.7
84.4
74.4
94.1
mean value of these concentrations calculated in MORB from a much larger set of
samples. Normalize the data for each sample to the mean value, plot the normalized
values against the atomic number, and use the results from the previous exercise to
infer whether fractionation is due to the precipitation of minerals in which these ele-
ments are in octahedral sites (e.g. olivine, pyroxene) or to minerals in which they could
also reside in tetrahedral sites (oxides).
8. The platinum-group elements (PGE) consist of the following transition elements: Ru
(44), Rh (45), Pd (46), Os (76), Ir (77), and Pt (78) with their proton numbers given in
parentheses. Discuss how to apply the crystal field theory to these elements and decide
what you need to know to understand their crystal chemistry.
9. Let the length of a polyhedron edge be a and the radius of the circumscribed sphere
be R . For a te tr ahedron it can be shown that R
4) a 6, while for an octahedron
=
(1
/
2) a 2. The ionic radius of O 2 is 1.4 Å. Calculate the radius of the cations
that closely fit in a tetrahedral or octahedral site. Compare with a table of ionic radii
(e.g. http://www.webelements.com ).
10. Using the data listed in Table 1.4 , draw a semi-logarithmic plot of the composition of:
(i) ordinary chondrites normalized to CI carbonaceous chondrites for decreasing
50 percent condensation temperature
(ii) continental crust normalized to the BSE or primitive mantle by decreasing values
of the normalized value
(iii) the primitive mantle normalized first to CI carbonaceous chondrites, then to
ordinary chondrites using the same order
(iv) a Hawaiian basalt and a mid-ocean ridge basalt normalized to primitive mantle
using the same order.
11. Using the first plot of the previous exercise, try to evaluate the condensation tempera-
ture of the elements for which this parameter is missing.
12. Using all the plots and a periodic table, find which group of elements trivalent yttrium
(Y) is homologous to. Then do the same for thorium (Th) and uranium (U).
R
=
(1
/
 
 
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