The Sterling Mine closed in 1986 after yielding 11 million tons of zinc, iron, and manganese ore. Together with the nearby Franklin Mine, it had a huge impact on the economic and cultural development of Sussex County, as many immigrants came there to work. These orebodies and the enclosing Franklin Marble constitute one of the great mining districts of the world and have yielded more than 380 mineral species, more than 90 of which fluoresce under ultra violet light. The Sterling Mine has been preserved as the Sterling Hill Mining Museum, whose mission is to share this geological and mineralogical treasure with future generations.