The results of the molar calculations must next be recalculated on the basis of a number of oxygens or of cations in the structural formula of the mineral. A conversion factor, is needed to convert the total of cations (or oxygen) to the number appropriate for a given mineral. Values for some minerals are:
Numbers of Oxygens or Cations for Normalization
|
Mineral |
Oxygens |
Cations |
|
Mineral |
Oxygens |
Cations |
|
Amphibole |
23 |
|
|
Andalucite |
20 |
|
|
Apatite |
25 |
|
|
Biotite |
11 |
|
|
Carbonates |
6 |
|
|
Chlorite |
14 |
|
|
Epidote |
13 |
|
|
Feldspar |
8 |
|
|
Garnet |
12 |
|
|
Kyanite |
5 |
|
|
Muscovite |
11 |
|
|
Olivine |
4 |
|
|
Pyroxene |
6 |
|
|
Sillimanite |
5 |
|
|
Sphene |
|
12 |
|
Spinel |
4 |
|
|
Topaz |
20 |
|
|
Vesuvianite |
|
50 |
|
Wollastonite |
18 |
|
|
Zircon |
16 |
|
For example, recalculation of feldspar analyses is done on an 8-oxygen basis; thus , the conversion factor is 8 divided by the total moles of oxygen. All the cation (or oxygen) values are multiplied by the appropriate conversion factor to yield normalized molar amounts. In addition, if the concentrations of F and/or Cl have been determined, their abundances are divided by atomic weight (18.9984 and 35.453, respectively) and multiplied by the same conversion factor.
Back: 6.2.1. Calculating Moles of Cations or Anions | Next: 6.2.3. Assigning Cations to Crystallographic Sites | Home: Course Overview
Copyright 1997-2003, James H. Wittke
Last update: 01/18/2006 01:47 PM.