Willemite, Franklinite and Zincite- The Trio of Classic Ore Minerals from the Franklin Mine
Willemite, franklinite and zincite represent the three most important zinc-bearing minerals mined at the Franklin Mine, Franklin, New Jersey. Franklinite is a black-colored zinc iron oxide mineral that is never fluorescent. Zincite is a zinc oxide that sometimes shows a yellow fluorescent response under long wave UV, but often is not fluorescent. Willemite, a zinc silicate, is one of the brightest fluorescing minerals from the Franklin Mine, showing a bright green response under short wave UV, sometimes with long-lasting green phosphorescence. Sometimes it also shows a respectable green response under long wave UV. The specimen featured here, from the Franklin Mine, Franklin, Sussex County, New Jersey, contains all 3 zinc-bearing minerals, but only the willemite is fluorescent. The size of this piece is 72 x 61 x 46 mm, and it weighs 304 grams.
In the above photograph, the willemite shows brilliant green fluorescence under short wave UV (254 nm).
Following exposure to short wave UV (254 nm), bright and lasting green phosphorescence/afterglow is seen.
Under long wave UV (365 nm) a similar, but less bright green fluorescent response is seen.
Same specimen shown under visible light. The willemite is present as large apple green grains. The franklinite is the black-colored mineral. Minor amounts of red-brown zincite are also visible.