51 Mineral Components

The Geology and Petrography of Crater Lake National Park, 1902

 PART II.

HYPERSTHENE-ANDESITES.

MINERAL COMPONENTS.

The phenocrysts of these rocks are basic plagioclase, hypersthene, augite, and magnetite. The last-named mineral, to be sure, does not appear as a phenocryst in the hand specimen, but it is always present and belongs in part to the crystallizations of the first generation. To the above should be added olivine and hornblende, which are very seldom present.

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