Mining Engineering Board Practice Exam

Andesite is an igneous volcanic rock that is primarily composed of plagioclase and hornblende. Plagioclase is a key mineral found in andesite, contributing to its intermediate composition between basalt and rhyolite, while hornblende (a type of amphibole) adds to its mineral diversity and is commonly present in volcanic rocks.

This specific mineral combination gives andesite its characteristic gray color and fine-grained texture, which are visible when observing the rock. The presence of these minerals is indicative of the processes involved in the rock's formation, where moderate thermal conditions allow for the crystallization of these minerals as magma cools.

Other options mentioned contain minerals that are either not typical of andesite or are more commonly associated with other igneous rock types. For instance, olivine and pyroxene are more associated with basalt and mafic rocks, while quartz and K-feldspar are prevalent in more silica-rich rocks like granite or rhyolite. Ca-plagioclase and olivine are also more indicative of specific basaltic compositions.