Columbia subject headings:
Harvard subject headings:
Sulfur industry--Italy--Caltanissetta (Province)--History.
Sulfur miners--Italy--Caltanissetta (Province)--History.
Sulfur mines and mining--Italy--Caltanissetta (Province)--History.
Princeton subject headings:
Social conflict--Italy--Sicily--History.
Sulfur miners--Italy--Sicily--History.
Sulfur mines and mining--Italy--Sicily--History.
Zurli, Mario--Career in mining.