Table 3. Microprobe analytical compositions of amphibole.

[Oxide values are in weight percent; n.a., not analyzed]

Rock type
Sample

Dacite Pt16

Andesite Pt43
core

Basalt Pt53

Core

Cummingtonite rim

Core

Rim

Olivine rim

SiO2

45.02

52.59

49.67

40.85

39.88

40.88

TiO2

1.67

.34

.76

1.57

1.59

1.66

Al2O3

12.53

2.53

5.87

14.43

13.89

13.87

MgO

15.06

20.98

15.63

14.49

14.98

15.52

CaO

10.95

1.66

10.51

11.72

11.59

11.00

MnO

.15

.96

.66

.22

.16

.15

FeO

10.45

17.69

13.39

11.89

11.80

11.48

Na2O

2.26

.47

1.16

2.72

2.59

2.62

K2O

.46

.02

.22

.83

.75

.75

F

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

Cl

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

H2O calculated

2.09

2.08

2.07

2.05

2.01

2.04

     Total

100.64

99.32

99.94

100.77

99.24

99.97

Number of cations on the basis of 23 oxygens

Si

6.462

7.592

7.209

5.983

5.938

6.010

Al

2.119

.430

1.004

2.491

2.437

2.403

AlIV

1.538

.408

.791

2.017

2.062

1.990

AlVI

.581

.023

.213

.473

.376

.412

Ti

.180

.037

.083

.173

.178

.184

Mg

3.223

4.517

3.383

3.165

3.326

3.402

Ca

1.684

.257

1.634

1.839

1.849

1.732

Mn

.018

.117

.081

.027

.020

.019

Fe

1.255

2.138

1.627

1.458

1.471

1.413

Na

.629

.132

.326

.772

.748

.747

K

.084

.004

.041

.155

.143

.141

Sum

17.774

15.654

16.393

18.553

18.547

18.141

This page is <https://pubs.usgs.gov/pinatubo/bernard/table3.html>
Contact: Chris Newhall
Last updated 03.29.99