Green mica
schist
This is a low grade metamorphic rock formed from a shale
or mudstone. It is coarser grained than the slate, and consists of
alternating thin layers of mica and quartz. The platy mica
crystals are aligned parallel to each other, giving the rock
a schistosity (the coarser-grained equivalent of the slate's
cleavage) and the rock tends to break easily along this
direction. In this sample the schistosity has also been bent
into small folds. The greenish colour is due to the green
mineral chlorite, a soft platy mineral similar to mica.