20 coals from different Saarland pits. The pieces of coal originate from the Helene pit, Dechen pit, König pit, Maybach pit, Frankenholz pit, Wellesweiler pit, from the Saar/North Shaft mine, Reden mine, Warndt mine, St. Ingbert mine, Göttelborn mine, Luisenthal mine and Camphausen mine.