Open formations colonizing heavy metal soils, either natural or resulting from past mining operations, in rapid regression and limited to a few stations in eastern Belgium, western Rhineland, Westphalia and Lower Saxony, and to one station in the southern Netherlands, with outposts in northern France, comprised of a highly specialised flora with the endemics Viola calaminaria, Viola guestphalica, Thlaspi caerulescens (Thlaspi alpestre ssp. calaminare) and Festuca aquisgranensis (Festuca ophioliticola ssp. calaminaria), with Minuartia verna var. hercynica, Silene vulgaris ssp. humilis and Armeria halleri, limited to this formation and the next, and with the steppic, central European Festuca valesiaca.