Esperite, Willemite, Calcite
Esperite: fluorescent yellow, SW
Willemite: fluorescent green, SW
Calcite: fluorescent red to orange-red, SW
Franklinite: non-fluorescent
Zincite: non-fluorescent

Esperite {PbCa3Zn4(SiO4)4} is a very rare mineral that fluoresces a beautiful canary-yellow color under shortwave UV.  Thus far it's been found in significant amounts only at Franklin, New Jersey.  Even there it doesn't exactly grow on trees, although untold tons may lie buried in old, flooded mine stopes beneath the town of Franklin.  Bob's Rock Shop website indicates that micro crystals of esperite have also  occurred at El Dragon Mine, Potosi, Bolivia.

Esperite is exceedingly rare worldwide.  Not even Sterling Hill, just a couple of miles down the road from Franklin, produced this mineral.

The specimen shown above is about 3 inches across in largest dimension.  I bought it from Nick Zipco when he used to sell minerals from his car in the museum parking lot.

Esperite was formerly known as "Calcium-Larsenite", and you might see it labeled as such in older collections or books.

Esperite is a lead-silicate mineral that came from a certain region of the mine. Typical associations are willemite, calcite, garnet, zincite, hardystonite, larsenite, and franklinite. Why doesn't esperite occur more often?  For some reason, silicates containing lead as a primary element seem to be quite rare overall (e.g., esperite, margarosanite, hancockite, roeblingite). A mineralogist could tell you more about the specific reason;  generally speaking, it seems the conditions in the earth do not often favor the formation of these minerals.

Ask a typical Franklin mineral collector what they'd look for if they had unlimited resources and could dig up any area of the earth.  Forget the gold and diamonds;  gold doesn't fluoresce under UV, and diamonds are just carbon. Admittedly, they are useful in that one could sell them and buy some good Franklin rocks.

Having just won that mythical mega-lottery and being able to convince the appropriate bureaucrats to issue the mining permits, any Franklin collector worth his basement full of rocks would choose to mine the earth for esperite, margarosanite, roeblingite, and the rest of the "Parker suite".   Franklin would reopen as a mining town.  Gigantic water pumps would roar back to life.  There'd be no more big-box superstores, except ones that sold mining equipment, Gatorade, and camping supplies.  Wal-Mart could probably stay, because it doesn't sit atop the actual mine area or mineral dumps.  Then again, maybe it would have to be bulldozed to make room for a mineral dump. 

Incidentally, John Cianciulli once told me there's a Franklin-like ore deposit underneath a certain town in Warren County, New Jersey.  I don't know any more about this right now but would certainly like any information on it that might be available.

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