Geology Reference
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appear in enough concentration within the crust to form mineral phases in their
own right. Instead they usually replace major elements in crystal structures
10
.
Consequently, based on Grigorev's analysis, a new mineralogical composition of
the upper continental crust
P
i=1
^
i
was calculated. Since there are not as many
equations as unknowns, a reasonable number of additional hypothesis had to be
formulated. Accordingly, the model was optimised in order to satisfy the following
requirements (Valero D. et al., 2010a):
(1) The mass balance between compounds and elements, i.e.
P
j
r
j;i
^
i
= ^
j
, with
^
j
representing the chemical composition of the upper crust determined as by
Rudnick and Gao (2004).
(2) The mass content of every mineral in the crust must always be greater than
zero, i.e.
^
i
> 0.
Additionally, if constraints 1 and 2 were satisfied, the relative proportions of
the minerals in Grigorev's model were kept constant. Moreover, if an important
11
mineral of a certain element was absent in Grigor'ev analysis, it was included by
the authors, making reasonable assumptions
12
on its abundance based on existing
literature.
Table 10.5 shows the crepuscular crust, which coincides with the mineralogical
composition of the upper Earth's crust. The model obtained contains 324 species,
57 more than in that of Grigor'ev (2007). Of the 324 substances 292 are minerals.
The rest are predominately diadochic elements included in the crystal structure of
other minerals, as is the case for the following elements: Ce, Nd, Ni, Y , Rb, Co,
Dy, Er, Eu, Ga, Gd, Ge, Ho, Lu, Re, Sc, Tb, Tl, Tm, V , Hf, In, Pd, Pr, Pt, Rh,
Ru, Sb, Se, Sm, Te, Y b. The resulting molecular weight of the upper continental
crust is 155.2 g/mole. Details of the procedure (with a description of the specific
optimisation method for each element) and a discussion of the results are described
in Valero D. et al. (2008, 2010a).
Table 10.5: Mineralogical composition of the crepuscular crust
Mineral
Formula
mass, %
Quarz
SiO
2
2.29E+01
Albite
NaAlSi
3
O
8
1.35E+01
Oligoclase
Na
0:8
Ca
0:2
Al
1:2
Si
2:8
O
8
1.19E+01
Orthoclase
KAlSi
3
O
8
1.18E+01
Andesine
Na
0:6
Ca
0:4
Al
1:4
Si
2:6
O
8
5.46E+00
Paragonite
NaAl
3
Si
3
O
10
(OH)
2
3.96E+00
KMg
2:5
Fe
2+
0:5
AlSi
3
O
10
(OH)
1:75
F
0:25
3.82E+00
Biotite
K
0:6
(H
3
O)
0:4
Al
2
Mg
0:4
Fe
2+
0:1
Si
3:5
O
10
(OH)
2
3.03E+00
Hydromuscovite/
Illite
Continued on next page :::
10
The ability of certain different elements to exist in place of each other in certain points of a
space lattice is called Diadochy.
11
A mineral is considered important, should it constitute an ore of a certain element.
12
The assumptions are explain in detail in Valero D. et al. (2008).
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