Biotite gneiss;
Loch Laxford, NW Scotland
This rock is mostly composed of creamy-white feldspar and
quartz, together with dark minerals, of which the most
abundant is the dark mica biotite. The dark minerals are
arranged in a streaky banding, giving the rock a gneissic
texture. The flakes of mica are also aligned with their long
dimensions parallel to the mineral banding. However, the
rock is not fissile, i.e. it does not break easily along
this direction. Therefore, despite its mica content, it
would not be called a schist.