Hardystonite, clinohedrite, willemite
Hardystonite: fluorescent blue-violet
Clinohedrite: fluorescent orange
Willemite: fluorescent green
Calcite: fluorescent red
Franklinite: non-fluorescent regions

Hardystonite {Ca2ZnSi2O7} is a classic Franklin mineral that fluoresces blue-violet under shortwave UV. It sometimes fluoresces under longwave, too, but it's not as intense. Though its formula may not look all that exotic, hardystonite is quite rare worldwide.  In fact, it is considered unique to Franklin;  the only other hardystonite occurrence of which I'm aware is micro crystals in some slags in Germany.  (Slag minerals are in a sense man-made, because they are the result of human activity.)  

Within Franklin, hardystonite occurs in small amounts on the Buckwheat Dump, though the Trotter Dump appears to have some potential as well.   Hardystonite occurred in the Franklin ore body but did not, as far as anyone knows, occur at Sterling Hill.   Today, much of the hardystonite at Franklin has been re-buried or else lies deep in flooded mine stopes;  looking at early photos of the town, one can see that Franklin was virtually one, big tailings pile.  Gradually the rock piles disappeared forever beneath houses, roads, parking lots, and so forth.  

Later in the mining operation it was also deemed more cost-effective to backfill depleted mine workings with waste rock instead of dumping the rock on the surface.  

Clinohedrite {CaZnSiO4.H2O}, another rare mineral, is an alteration product of hardystonite, but this alteration occurs in the ground at some point in the formation of the hydrothermal deposit-- not on the earth's surface as the typical weathering "alteration" we think of.  Clinohedrite does sometimes occur without hardystonite; I've seen specimens where clinohedrite formed a coating on a willemite / andradite matrix. I'm not sure if hardystonite had accompanied it at one time in the geologic history or not.

Photo is shown here with permission. The specimen shown above is now in a private collection.

One can only imagine how many tons of hardystonite and other exquisite minerals are buried beneath Franklin.  We are fortunate, however, that some of these minerals did stay on the surface and remained available so that collectors could preserve them.    

It is important to understand one thing about Franklin minerals (actually, minerals in general):  much of what you see in museum cabinets was obtained only because some miners were willing to violate company policy and carry out specimens secretly (often, literally hidden in lunchboxes).  Many other specimens were obtained by collectors who, especially in today's view, were a nuisance to the people who want nothing more from life than strip malls, condos, and parking lots. 

Without these miners and collectors, there wouldn't be much to see in the mineral museums.  I'm going to make a fairly bold statement here, but I'm pretty sure it's true:  on the whole, the mineral heritage of Franklin and Sterling Hill has been preserved by dedicated amateurs.  

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