Close up of perpendicular feldspar rock near the western margin of the
Skaergaard intrusion, Mellemø. The rock is defined by branching
crystals of plagioclase feldspar directed inwards toward the centre of
the intrusion. The rock is commonly taken as a good illustration of heterogeneous
crystal nucleation and growth on a solid surface. The crystallisation is
probably closely related to volatile fluctuations. Photo by Jens C. Andersen.