Exsolution Willemite & Calcite

Exsolution willemite is very unusual at the Buckwheat... or it was until we dug up a few good-sized chunks of it, associated with calcite, pyroxene, and an unknown subtranslucent brown mineral with an intense resinous luster similar to that of triplite (I say that because I'm looking at a piece of triplite from Argentina which could be the spittin' image). 

Everyone I've talked to says this resinous mineral has to be tephroite for some vague reason or another, but I have this theory that it might be fayalite

This idea is near-blasphemy to most Franklin collectors I've talked to, but I plan to do some tests if I ever get around to it.  Recall that fayalite and tephroite form a series.  Tephroite and willemite form another series.  Recall also that fayalite was found in the Buckwheat tunnel that went from the Buckwheat pit to the dump, and undoubtedly some of that rock found its way onto the dump (see the Dunn monograph on the Franklin-Sterling Hill minerals).  Now, I ask you:  why couldn't some of this fayalite contain willemite? 

Here's another clue:  the willemite's fluorescence is not nearly as bright as usual.  It's sort of like the "black willemite" from Sterling Hill which occurs with... guess what... fayalite. 

There is still much on the mineral dumps that has escaped study. 

This particular assemblage was overlooked in all the studies I know of, so I am not 100% confident when I'm told it must be tephroite.  At least I doubt that it's end-member composition.  I just have a feeling it has some iron in it (easy enough to determine with simple chemical tests).

The blue you see in the photograph seems to be reflected visible light from the UV lamp. However, even in real life you sometimes see a bit of blue "fluorescence" in the vitreous matrix that the willemite runs through. I think it's some type of weird reflection, but I'm still not 100% sure.

I've seen this material on the Trotter Dump as well as the Buckwheat.  It is very interesting stuff.


Light used: Superbright 2000SW. Film & camera settings: Shop-Rite 400 speed film; exposure time 2 seconds; f-stop 5.6; minor gamma reduction applied to scanned image. 

If time permits I'll take a better, larger photo of this specimen.

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