Which igneous rock contains the greatest amount of quartz?

yes

NO. It helps form igneous rocks like granite along with mica and feldspar and other minerals, in basalts and gabbros there is no quartz but it does form silicates like olivine.

When weathered out of igneous rocks like granite it will eventually be found on beaches as sand grains.

It is found in metamorphic rocks where it usually forms large lenses, and in fault systems as masses of quartz and other churned up rock powder. It forms the major gangue or waste mineral in many metal mines.