Granite

The photograph above is under crossed polarizers. The field of view is about 4 mm. The mineral with numerous crossing twins is microcline. The clear (white), anhedral mineral is quartz. The partially altered, smaller grains are plagioclase, and the bright mineral in the upper right is biotite. This is a typical mineral assemblage in granites.

Occurrence:

Granites are abundant in continental shield areas and in deeply eroded folded mountain belts.