The calculation of mineral chemistry from probe analyses entails the conversion of oxide data to moles of cations and oxygen and then renormalization on the basis of a given number of cations or oxygens. In the procedures described the oxidation state of Fe is ignored.
To determine the mole of cations present, one divides the measured oxide weight percents by the cation-equivalent molecular weights given in the table below. These numbers take into account the fact that some oxides contain two or more cations.
Moles of oxygen are calculated assuming that all cation are bonded to oxygen. Thus, we may simply multiply the moles of cations by the oxygen factor to get moles of oxygen.
Single-Cation Molecular Weights and Oxygen Factors
|
Oxide |
Molecular |
Oxygen |
|
Oxide |
Molecular |
Oxygen |
|
Oxide |
Molecular |
Oxygen |
|
Al2O3 |
50.9806 |
1.5 |
|
BaO |
153.3394 |
1 |
|
CaO |
56.0794 |
1 |
|
Ce2O3 |
164.1191 |
1.5 |
|
Cr2O3 |
75.9951 |
0.5 |
|
Cs2O |
140.9051 |
0.5 |
|
EuO |
167.9594 |
1 |
|
Fe2O3 |
79.8461 |
1.5 |
|
FeO |
71.8464 |
1 |
|
Gd2O3 |
181.2491 |
1.5 |
|
HfO2 |
210.4888 |
2 |
|
K2O |
47.0977 |
0.5 |
|
La2O3 |
162.9046 |
1.5 |
|
Li2O |
14.9407 |
0.5 |
|
MgO |
40.3044 |
1 |
|
Mn2O3 |
78.9371 |
1.5 |
|
MnO |
70.9374 |
1 |
|
Na2O |
30.9895 |
0.5 |
|
Nb2O5 |
132.9049 |
0.4 |
|
Nd2O3 |
168.2391 |
1.5 |
|
NiO |
74.7094 |
1 |
|
P2O5 |
70.9723 |
0.4 |
|
PbO |
223.1994 |
1 |
|
Pr2O3 |
164.9068 |
1.5 |
|
Rb2O |
93.4675 |
0.5 |
|
SiO2 |
60.0848 |
2 |
|
Sm2O3 |
174.3991 |
1.5 |
|
SrO |
103.6194 |
1 |
|
Ta2O5 |
220.9464 |
0.4 |
|
TiO2 |
79.8988 |
2 |
|
UO2 |
270.0278 |
2 |
|
V2O3 |
74.9405 |
1.5 |
|
V2O5 |
90.9399 |
0.4 |
|
Y2O3 |
112.9050 |
1.5 |
|
ZrO2 |
123.2188 |
2 |
|
|
|
|
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Copyright 1997-2003, James H. Wittke
Last update: 01/18/2006 01:47 PM.