CIPW norms: Linking chemistry and mineralogy
I. Manual calculations of CIPW norms
Using the attached procedure and table, calculate CIPW norms for the following two
samples:
Sample 1 Sample 2
SiO2 61.52 51.7
TiO2 0.73 0.9
Al2O3 16.48 19.3
Fe2O3 1.83 1.1
FeO 3.82 4.8
MnO 0.08 0.2
MgO 2.80 1.1
CaO 5.42 4.1
Na2O 3.63 8.9
K2O 2.07 4.6
P2O5 0.25 0.30
Explain why it is not possible to have both quartz and olivine, or quartz and
feldspathoids, in the same rock.
II. Norms and minerals
Use now the excel file available to you, either on the computer in the prac. room or on
webCT (cipw-simple.xls). This file allows you to calculate norms for reasonable
compositions (don’t expect it to work perfectly for “weird” compositions, though).
Enter the major elements composition at the top (“bulk analysis”, yellow) and read the
results in the weight proportion area (green).
A. Exploring the relations between chemistry and (normative)
mineralogy
(based on a problem by J.D. Winter, p.152)
1. Calculate a norm using the composition below (a average basalt), and note the
resulting normative minerals. Determine the plagioclase composition. Is this
mineralogy consistent with a basalt?
2. Now vary the silica content in successive 1% increments between 46 and 52%.
Explain the effects it has on normative minerals.
3. Return to your initial SiO2 value, and vary Al2O3 between 14 and 19%.
Explain the effects on the norm.
4. Return again to your original value, and increase Na2O from 1 to 5%. Explain
the changes.
5. Then, do the same for K2O.
Basalt
SiO2 49.2
TiO2 0.19
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