Fensterquartz

Fensterquartz crystals were formed by a sudden drop in pressure in the crystal fissure, triggered by tectonic movements. In the process, the crystal building blocks were generally deposited at the crystal edges, while the filling of the surfaces was lacking. This shear or skeletal growth led to the formation of cavities that protrude into the crystal like open pits, preferably on the prism faces. Pocket clay enclosed in the crystals brings out the window effect particularly well. Fensterquartz often crystallises as double terminated crystals.

Photo: Quartz (window quartz), Val d’Illiez VS, collection Felix Spahr; not on sale.