Chemistry Reference
In-Depth Information
depending on whether the beam is perpendicular or parallel to cleavage,
the measures of the elements located in the interlayers may be different;
biotites are sometimes slightly chloritized with some leaching of potas-
sium, even if they appear optically fresh;
it is better to avoid to take into account K, Na, Ca in the calculation of
the structural formula.
Micas are not strictly dioctahedral or trioctahedral because there is
some extent of solid solution between the end members. The number of
cations in the cell is not known.
Table 4.
Example of a mineral with ferric and ferrous iron and water a hornblende
A
0-1
X
2
Y
5
Z
8
O
22
(OH)
2
.
Wt %
Results of the
microprobe
Recalculated
analysis
Structural formula
SiO
2
42,35
42,35
Si
6,28
Z site (8)
TiO
2
0,39
0,39
AI
IV
1,72
AI
2
O
3
16,25
16,25
total AI
2,84
Cr
2
O
3
0,91
0,91
AI
VI
1,12
FeO*
16,55
Ti
0,04
Fe
2
O
3
3,72
Cr
0,11
FeO
13,21
Fe
3
+
0,41
MnO
0,28
0,28
R
3
+
1,68
Y site (5)
MgO
7,46
7,46
Fe
2
+
1,64
CaO
11,12
11,12
Mn
0,04
Na
2
O
1,70
1,70
Mg
1,65
K
2
O
0,47
0,47
R
2
+
3,32
BaO
0,00
0,00
Ca
1,77
A (2) and
X (0,34) sites
F
0,00
0,00
Na
0,49
CI
0,00
0,00
K
0,09
H
2
O
2,02
Ba
0,00
total
97,48
99,88
Ca
+
Na
+
K
+
Ba
2,34
OH
2,00
OH
+
F
+
CI
=
2
F
0,00
CI
0,00
Parameters of the calculation.
Number of cations others than Ca, Na, K
=
13.
Number of oxygens corresponding to the other cations
=
21.
OH
+
F
+
CI
=
2
Total iron
=
Fe
2
+
+
Fe
3
+
=
Fe
=
2,05.
Numbers of oxygens corresponding to the previous cations without taking into account.
The ferric-ferrous ratio
=
20,793.
Columns of intermediate calculations are omitted.
