Table 4. Microprobe analytical compositions of pyroxene.

[Oxide values are in weight percent; n.a., not analyzed; Wo, wollastonite; En, enstatite; Fs, ferrosilite]

Rock type
Sample

Clinopyroxene

 

Orthopyroxene

Andesitic pumice Pt41

 

Andesite Pt46

Andesite Pt46

core

rim

core

rim

core

rim

core

rim

#1

#2

#3

SiO2

52.57

50.74

51.54

 

49.53

53.09

52.43

51.92

52.10

 

55.04

55.64

56.09

TiO2

.19

.43

.35

 

.51

.18

.23

.26

.27

 

.02

.10

.04

Al2O3

1.89

3.60

3.00

 

4.01

1.90

1.91

2.24

2.24

 

.60

1.08

.50

Fe2O

2.88

3.14

2.44

 

4.65

2.28

2.57

3.34

3.49

 

.00

.00

.00

FeO

1.98

2.64

3.29

 

2.19

2.42

2.87

2.22

2.21

 

15.97

14.82

13.00

MnO

.12

.12

.15

 

.21

.12

.19

.14

.17

 

.66

.75

.59

MgO

17.93

15.62

16.71

 

15.51

17.79

17.42

17.70

17.37

 

28.72

24.48

30.71

CaO

21.83

22.65

21.62

 

22.12

22.04

21.73

21.59

21.92

 

.14

.89

.16

Na2O

.21

.31

.22

 

.28

.23

.19

.14

.24

 

.01

.21

.00

K2O

.00

.00

.00

 

.00

.03

.02

.03

.00

 

.00

.00

.00

Cr2O3

n.a.

n.a.

n.a.

 

n.a.

n.a.

n.a.

n.a.

n.a.

 

.00

.01

.01

     Total

99.61

99.24

99.31

 

99.01

100.08

99.57

99.58

100.01

 

101.16

97.99

101.09

Number of cations on the basis of 6 oxygens

Si

1.922

1.877

1.899

 

1.843

1.932

1.924

1.904

1.905

 

1.965

2.035

1.974

Ti

.005

.012

.010

 

.014

.005

.006

.007

.007

 

.001

.003

.001

Al

.081

.157

.130

 

.176

.081

.083

.097

.097

 

.025

.047

.021

Fe3+

.079

.087

.068

 

.130

.063

.071

.092

.096

 

.000

.000

.000

Fe2+

.060

.082

.101

 

.068

.074

.088

.068

.068

 

.477

.453

.383

Mn

.004

.004

.005

 

.007

.004

.006

.004

.005

 

.020

.023

.018

Mg

.977

.861

.918

 

.860

.965

.953

.968

.947

 

1.528

1.334

1.611

Ca

.855

.898

.854

 

.882

.859

.854

.848

.859

 

.006

.035

.006

Na

.015

.022

.016

 

.020

.016

.014

.010

.017

 

.001

.015

.000

K

.000

.000

.000

 

.000

.001

.001

.001

.000

 

.000

.000

.000

Cr

-

-

-

 

-

-

-

-

-

 

.000

.000

.000

Wo

43.3

46.5

43.9

 

45.3

43.7

43.3

42.8

43.5

 

.3

1.9

.3

En

49.5

44.6

47.2

 

44.2

49.1

48.3

48.9

47.9

 

75.3

72.3

79.7

Fs

7.2

9.0

8.9

 

10.5

7.2

8.4

8.3

8.6

 

24.5

25.8

19.8

Mg/(Mg+Fe)

87.6

83.4

84.5

 

81.3

87.6

85.7

85.8

85.2

 

75.46

73.70

80.07

This page is <https://pubs.usgs.gov/pinatubo/bernard/table4.html>
Contact: Chris Newhall
Last updated 03.29.99