Table 6. Microprobe analytical compositions of biotite.
[Oxide values are in weight percent; n.a., not analyzed]
|
Rock type |
Andesite |
|
Dacite (phenocryst) |
|
|---|---|---|---|---|
|
PIN6 |
Pt23 |
|||
|
|
3 |
4 |
||
|
SiO2 |
40.61 |
38.55 |
|
38.62 |
|
TiO2 |
.52 |
1.82 |
|
3.04 |
|
Al2O3 |
14.22 |
14.49 |
|
13.35 |
|
Cr2O3 |
.53 |
.20 |
|
n.a. |
|
FeO |
5.28 |
11.65 |
|
14.44 |
|
MnO |
.06 |
.12 |
|
.09 |
|
MgO |
24.31 |
18.82 |
|
17.59 |
|
CaO |
.00 |
.00 |
|
.00 |
|
Na2O |
.86 |
.78 |
|
.76 |
|
K2O |
8.90 |
8.66 |
|
9.06 |
|
H2O |
3.81 |
3.68 |
|
4.05 |
|
Total |
99.10 |
98.77 |
|
101.00 |
|
Number of cations on the basis of 22 oxygens |
||||
|
Si |
5.764 |
5.659 |
|
5.650 |
|
Ti |
.056 |
.201 |
|
.330 |
|
Al |
2.379 |
2.507 |
|
2.330 |
|
Cr |
.059 |
.023 |
|
n.a. |
|
Fe |
.627 |
1.430 |
|
1.770 |
|
Mn |
.008 |
.015 |
|
.010 |
|
Mg |
5.143 |
4.117 |
|
3.840 |
|
Ca |
.000 |
.001 |
|
.000 |
|
Na |
.236 |
.221 |
|
.220 |
|
K |
1.612 |
1.622 |
|
1.690 |
|
OH |
4.000 |
4.000 |
|
3.960 |
|
Total |
19.884 |
19.796 |
|
19.770 |
This page is <https://pubs.usgs.gov/pinatubo/bernard/table6.html>
Contact: Chris Newhall
Last updated 03.29.99