Geology 200: Balancing ionic charges in mineral formulas
Calculate the total number of positive charges for the cations and the total number of negative charges for the anions for each mineral formula. Also, list the charges for each individual element (periodic table, Fig. 3.3, p. 57 of text). An example for olivine is given below. Be able to do this for Test 1. Answers will be posted on the class web page. Do the exercise before checking the answers.
Cations + |
Anions - |
|
| quartz: SiO2 | 4 |
-4 |
Si = 4 |
O = -2 |
|
| calcite: CaCO3 | 6 |
-6 |
Ca = 2, C = 4 |
O = -2 x 3 |
|
| gypsum: CaSO4 | 8 |
-8 |
Ca = 2, S = 6 |
O = -2 x 4 |
|
| olivine: (Mg, Fe)2SiO4 | 8 |
-8 |
Mg or Fe = 2 x 2; Si = 4 |
O = -2 x 4 |
|
| pyroxene: (Mg, Fe)SiO3 | 6 |
-6 |
Mg or Fe = 2, Si = 4 |
O = -2 x 3 |
|
| plagioclase: NaAlSi3O8 | 16 |
-16 |
Na = 1, Al = 3, Si = 4 x 3 |
O = -2 x 8 |
|
| Plagioclase: CaAl2Si2O8 | 16 |
-16 |
Ca = 2, Al =3 x 2, Si = 4 x 2 |
O = -2 x 8 |
|
| K-feldspar: KAlSi3O8 | 16 |
-16 |
K = 1, Al = 3, Si = 4 x 3 |
O = -2 x 8 |
|
| muscovite: KAl3Si3O10(OH)2 | 22 |
-22 |
K=1, Al = 3 x 3, Si = 4 x 3 |
O = -2 x 10, OH = -1 x 2 |
|
| kaolinite: Al4Si4O10(OH)8 | 28 |
-28 |
Al = 3 x 4, Si = 4 x 4 |
O = -2 x 10, OH = -1 x 8 |