Quartz vein cutting Upper Salmian (Ordovician) Mn-rich metapelites (phyllades) (Hercynian metamorphism).
South Border of Stavelot Massif.
Ref.:
Pasero M., Reinecke T., Fransolet A. M. (1994): Crystal structure refinements and compositional control of Mn-Mg-Ca ardennites from the Belgian Ardennes, Greece, and the Western Alps. N. Jb. Miner., Abh., 166, 137-167.