66 Chemical Analyses of Andesites

The Geology and Petrography of Crater Lake National Park, 1902

 PART II.

HYPERSTHENE-ANDESITES.

CHEMICAL ANALYSES OF ANDESITES.

The analyses given in the following table are all of Crater Lake rocks, with the exception of the last, which is from Crater Peak, California, and is given for comparison. The analyses were made by the chemists of the United States Geological Survey. The numbers at the heads of the columns are the specimen numbers.

Analyses of Crater Lake andesites.
[Analyses by H. N. Stokes, except of 1829.]

  25. 26. 31. 68. 94. 1829.
SiO2 59.39 60.98 58.48 62.09 60.09 68.12
Al2O3 18.45 17.82 17.85 17.03 17.85 16.24
Fe2O3 1.79 1.83 2.67 2.38 2.03 1.26
FeO 3.90 3.33 3.29 2.69 3.45 2.08
MgO 3.13 2.67 3.61 3.08 3.50 1.35
CaO 6.29 5.73 6.81 5.65 6.28 3.80
Na2O 4.29 4.26 3.77 4.10 4.17 3.89
K2O 1.29 1.43 1.23 1.67 1.31 2.54
H2O- .10 .13 .34 .04 .12 .40
H2O+ .42 .45 .86 .13 .26  
TiO2 .41 .71 .69 .65 .54 .25
ZrO2 None. None. None. None. None.  
CO2 None. None. None. None. None.  
P2O5 .22 .17 .24 .19 .23 .14
SO3 None. None. None. None. None.  
Cl Trace. Trace. Trace. Trace. Trace. —-
F Undet. Undet. Undet. Undet. Undet. —-
S None. None. None. None. None. —-
Cr2O3 None. None. None. None. None. None.
NiO None. None. None. None. .05 —-
MnO Trace. Trace. Trace. Trace. Trace. .10
BaO .05 .06 .05 .07 .05 .09
SrO .04 .05 .05 .07 .05 .02
Li2O Trace. None. Faint tr. None. Faint tr. Trace.
   Total 99.77 99.71 99.87 99.84 99.98 100.28
No. 25. Hypersthene-andesite, hypocrystalline type, subtype A, west edge of Wizard Island. See page 86.No. 26. Hypersthene-andesite, hypocrystalline type, subtype A, rim, just south of The Watchman. See page 86.

No. 31. Hypersthene-andesite, hypocrystalline type, subtype A, at the lake level under Llao Rock. See page 86.

No. 68. Hypersthene-andesite, holocrystalline type, Palisades, under Round Top on the northeast portion of the rim. See page 88.

No. 94. Hypersthene-andesite, hypocrystalline type, subtype A, from a large dike entirely transsecting the rim between Glacier Peak and Llao Rock. See page 86.

No. 1829. Of the Cascade Range collection, a rock called by Mr. Turner a pyroxene-andesite, holocrystalline type. From Crater Peak, California. Analysis by W. F. Hillebrand, taken from Bull. U. S. Geol. Survey No. 60, p. 157, No. 19. See page 90.

It is a little surprising and also unfortunate that out of five specimens of andesite selected by Mr. Diller for chemical analysis four should turn out to belong to one type, and this not the most common one. It is surprising, because these specimens were selected with a view to representing typical occurrences. As the selection was made before an opportunity was given for microscopic study, it was impossible to distinguish the different types from the hand specimen alone.

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