Cuspidine{Ca8(Si2O7)2F4}:  FL Orange-Yellow SW
Calcite {CaCO3}: FL Red-Orange SW
Hardystonite:  FL Blue-Violet SW
Willemite:  FL Green SW
Glaucochroite:  non-fluorescent
Franklinite:  non-fluorescent

A few specimens of Cuspidine have come from the Buckwheat Dump at Franklin, but the mineral is still considered very rare.  It is quite hard to find.  Several days of searching may turn up only a speck of it.  A couple of people have gotten lucky and found fairly large "eyes" of it in rock.  In my opinion, cuspidine is much rarer than margarosanite.  Quantitatively speaking, there were quite a few specimens of margarosanite that came out of the Franklin Mine;  it's just that today they're being hoarded.  Cuspidine, on the other hand, is not even present in most Franklin collections I've seen.

I was lucky enough to have seen Nick Zipco's collection once, and I remember seeing a very large cuspidine.  It was really something.  Neither he nor anyone else at the time knew it was cuspidine;  only more recent tests on similar material confirmed the I.D.  Anyway, according to a story that Nick told me, he risked his life to get that specimen.  You see, according to Nick, he had lowered himself down over a sheer rock face, using ropes.  (Of course, it's always possible he found the piece on the Buckwheat Dump back in the 40's or 50's...)


 It is especially unusual to find cuspidine and hardystonite together in the same rock in appreciable amounts, as in the above specimen.

I have looked through tons and tons of rocks in search of this mineral.  It occurs with glaucochroite, which can be a clue in daylight that you've got the right assemblage.  And yes, glaucochroite does occur on the Buckwheat.

The beautiful 4-color fluorescent specimen shown above is now in someone else's collection.  (Yes, I often wish I still had this rock.  Alas, I had bills to pay...)



As a parenthetical note, it just occurred to me that there's another, fairly easy chemical test that would bolster a tentative I.D. of cuspidine (if fluorescence alone weren't enough), at least narrowing it down to fluorine-containing minerals.  Johnbaumite, though a member of the apatite group, contains no fluorine.   Nor does turneaureite.

The test in question would be the micro tube test for fluorine and fluorides (notice there are 4 fluorines in a molecule of cuspidine).   I have not tried this test yet on a cuspidine specimen.  Since it could theoretically be done with a capillary tube (steady hands!), it would only require a speck of mineral.  A 4- or 5-mm borosilicate tube sealed at one end might be a bit more manageable;  I was talking to Don Peck, fellow chemist and the author of The Rock Identification Key, and he recommends the 6x50 borosilicate culture tubes for closed-tube tests. 

Small glass tubes, closed at one end, are also used for the "arsenic mirror" test, which should be positive in the case of johnbaumite or turneaureite.  It can be tricky to get the mirror;  it works best when there is much As in the rock.  It is unfortunate that the test requires sacrifice of some of the mineral in question.

It does so happen that fluorescence tests alone are generally sufficient to identify cuspidine, even though I don't like to pass up a chance to roast something at 800 degrees C.

Pretty much every cuspidine specimen I've seen or heard of has the following fluorescent response:
Short-wave:  yellow, orange-yellow, or mustard color
Mid-wave:  lilac or pale violet




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