Andesitic

a dark-colored volcanic rock composed essentially of plagioclase feldspar and one or more mafic minerals, as hornblende or biot-te.
historical examples

it is composed of andesitic lavas of the augite type, is pierced by many fumaroles, and has a crater in the solfatara stage.
the solomon islands and their natives h. b. (henry brougham) guppy

these are characterized by igneous rocks of andesitic nature.
the avifauna of micronesia, volume 3 rollin h. baker

amongst them i may mention those of bougainville strait, which are composed of andesitic lavas of the hornblende type.
the solomon islands and their natives h. b. (henry brougham) guppy

the building fronts the west, and is constructed of an andesitic tuff of inferior quality and dark colour.
encyclopaedia britannica, 11th edition, volume 15, slice 3 various

great m-sses of granite, syenite and diorite were intruded at this period, and send tongues even into the andesitic tuffs.
encyclopaedia britannica, 11th edition, volume 2, slice 5 various

after the cessation of the andesitic eruptions, a quiescent period of great length ensued.
the yellowstone national park hiram martin chittenden

noun
a fine-grained tan or grey volcanic rock consisting of plagioclase feldspar, esp andesine, amphibole, and pyroxene
andesite
(ān’dĭ-zīt’)
a gray, fine-grained volcanic rock. andesite consists mainly of sodium-rich plagioclase and one or more mafic minerals such as biot-te, hornblende, or pyroxene. it often contains small, visible crystals (phenocrysts) of plagioclase. it is the fine-grained equivalent of diorite.