text: Jean Charles Galissard de Marignac (24 April 1817 &ndash; 15 April 1894) was a Swiss chemist whose work with atomic weights suggested the possibility of isotopes and the packing fraction of nuclei.  His study of the rare earth elements led to his discovery of ytterbium in 1878 and co-discovery of gadolinium in 1880.
  He was considered "one of the great chemists of the nineteenth century", particularly in the area of inorganic chemistry.
  On 13 September 2011, the site of his laboratory at the University of Geneva was designated a historical chemical landmark of Switzerland.