Calcareous tufa springs are rare and special habitats that are home to a variety of specialised creatures and are protected EU-wide protection (FFH Directive). At the source of the spring, lime is deposited from the water, forming the porous calcareous tufa, one of the youngest rocks in the region. The lime, which glues the individual quartz grains together in the Luxembourg sandstone, was previously dissolved out by the water on its way through the sandstone.
This spring here in the valley of the Black Ernz lies several metres above the course of the stream. The water is artificially channelled from the spring over the rock and trickles down it. The calcareous tufa forms on the rock.