Here's why:
* Quartz is a major component of granite. Granite is a felsic igneous rock, meaning it is rich in silica (SiO2). Quartz is a form of silica, and it makes up a significant portion of granite's mineral composition.
* Other felsic rocks also contain quartz. Other felsic rocks like rhyolite, which is granite's extrusive counterpart, also contain high amounts of quartz.
* Quartz is less common in mafic and ultramafic rocks. Mafic and ultramafic rocks, like basalt and gabbro, have lower silica contents and therefore contain much less quartz.
In summary, granite is the igneous rock that is most likely to have the highest percentage of quartz.
