Andesite

Definition and stakes

Portrait of Charles Darwin Charles Darwin,  Coral Reefs; Volcanic Islands; South American Geology…

“ In three places [X, Y, Z] masses of andesite are exposed: at [Y] , this rock contained some quartz, but the greater part consisted of andesitic porphyry, with only a few well-developed crystals of albite, and forming a great white mass, having the external aspect of granite, capped by much dark unstratified porphyry. In many parts of the mountains, there are dikes of a green colour, and other white ones, which latter probably spring from underlying masses of andesite. ”
Source: Gutenberg

Portrait of Charles Darwin Charles Darwin,  Geological Observations on South America

“ These andesitic rocks form mountain masses of a white colour, which, in their general outline and appearance—in their joints—in their occasionally including dark-coloured, angular fragments, apparently of some pre-existing rock—and in the great dikes branching from them into the superincumbent strata, manifest a close and striking resemblance to masses of common granite and syenite: I never, however, saw in these andesitic rocks, those granitic veins of segregation which are so common in true granites. We have seen that andesite occurs in three places in Tierra del Fuego ”
Source: Gutenberg

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