What phenocryst minerals would you expect to find in a porphyritic andesite?
A) Ca- rich plagioclase and olivine
B) muscovite and biotite
C) intermediate (Ca- Na) plagioclase and amphibole or pyroxene
D) Na- rich plagioclase and K- feldspar

Question

Quizplus · Accepted Answer

Andesite is an intermediate volcanic rock, and porphyritic andesite typically contains phenocrysts of intermediate plagioclase (a mix of calcium and sodium) along with amphibole or pyroxene. These minerals reflect the intermediate composition of andesite, which is between basalt and rhyolite in terms of silica content.

What Phenocryst Minerals Would You Expect to Find in a Porphyritic