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Formulation

Calculations outline:

 
 		Method
 		Example
oxide name
 from data

SiO2

weight%
 from data

43.5%

mol wt.
 from periodic table

60.02

mol prop.
 (weight%) / (mol wt.)

.7248

cation prop
 (mol prop.) x (# cations in oxide)

.7248

oxygen prop.
 (mol prop.) x (#oxygen in oxide)

1.4496

cations on basis of # of O
(e.g., 12) 		(correction factor**) x (cation prop.)
(e.g., for a correction factor = 1.699)

1.231

cation assignment
 from radius ratio

4 CN

**Correction factor = (# of oxygens in ideal formula) / (sum of oxygen props.)

*Remember to check for electroneutrality

Formulation example:

Mineral: Olivine - ideal formula (Fe,Mg)2SiO4

Oxide
Name

SiO2

FeO

MnO

MgO

Total

Weight
Percent

34.96

36.77

0.52

27.04

99.29

Mol.
Prop.

0.5818

0.5118

0.0073

0/6708

 

Cation
Prop.

0.5818

0.5118

0.0073

0.6708

 

Oxygen
Prop.

1.1636

0.5118

0.0073

0.6708

2.3535

**Cats on
basis of 4

0.989

0.870

0.012

1.140

 

CN
Site

4 CN

6 CN

6 CN

6 CN

 

    **Correction factor = (# of oxygens in ideal formula) / (sum of oxygen props.)
      e.g., for olivine: # of oxygen in ideal formula = 4
        in the table above, the sum of the oxygen proportions for all of the oxides came to 2.3535

        Then the correction factor would be (4) / (2.3535) = 1.699

The composition of the above olivine would then be:

    (Mg1.14Fe0.87Mn0.01)Si0.99O4

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