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.
Looking at granite between crossed polarisers makes it
easier to distinguish the individual crystals. The rock is
made up of interlocking rectangular feldspars and
irregular clear quartz, all in shades of dark grey through
to white. The crystals showing yellow colours are mica
(muscovite) and tourmaline. Field of view 8 mm,
polarising filters