FL Blue to violet-blue SW
FL Orange SW
Calcite (or possibly
roeblingite?): FL Red to pinkish-red SW
FL Green SW
Manganaxinite: Non-FL; pale amber
to honey-yellow in daylight
Non-FL; brown in daylight
Copper: Non-FL; tiny specks visible with a loupe
No, the fluorescent violet-blue material in the photo above is not
hardystonite. It is xonotlite. Sometimes the difference in
fluorescent colors between the two minerals is minor, despite claims
from some collectors that "mineral A always fluoresces a particular
shade of purple, mineral B always fluoresces a distinct shade of
blue". Xonotlite's SW response does tend more toward blue, but it
isn't free of purple. An experienced collector can still tell it
from hardystonite in most cases. The associations and habit are
also important clues. (The presence of clinohedrite, by the way,
does not distinguish xonotlite from hardystonite; clinohedrite
can accompany either mineral.)
Xonotlite sometimes occurs as seam coatings in manganaxinite,
hyalophane, celsian, or andradite. Such coatings may be only
fractions of a millimeter thick. Under a microscope these seam
coatings may reveal themselves as layers of tiny, thin crystals.
||Left: the same specimen in
normal light. The xonotlite is a thin coating covering most of a
Matrix is mostly manganaxinite, which in this case has no noticeable
fluorescence. The axinite does have some specks of native copper
in it, however.
Even the weakest acids, including vinegar, will dissolve thin layers of
xonotlite; therefore, don't use vinegar or other acids to clean
specimens having thin seam coatings or fine crystals of this
mineral. It seems to be every bit as soluble as clinohedrite,
Xonotlite can also occur as massive, dull-white to gray material,
usually with hendricksite mica and sometimes with hancockite.
This massive xonotlite may contain small specks or larger spots of
Some Franklin xonotlite resembles cracked plaster in the
daylight. This is a classic habit for the Franklin
occurence. One such specimen I have that fits this description is
in a matrix of andradite
garnet, though there are no other fluorescent minerals (except
willemite) associated with it.
Finally, xonotlite may occur as white crystals, usually tiny and
occurring within a porous matrix of Parker shaft minerals (altered
hancockite, ganophyllite, etc.). Dr. Dunn's monograph (1995)
describes this assemblage.
The specimen pictured above contains some red- to
pinkish-red-fluorescing areas that may be either calcite or
roeblingite. Under the microscope these areas do not have the
typical appearance of calcite. They consist of tiny
crystals, but they have some curvature and are not well-formed.
They are subtranslucent and colorless to pale gray. They have the
brief intense phosphorescence (BIP) or "flash" in short wave UV,
meaning they're probably not axinite. I need to test these for
lead and perhaps for sulfate ions. Unfortunately the tests
some sacrifice of material, and I don't have much.
Calcite has the confusing habit of infiltrating other minerals and
making them appear to be something else; I've seen
calcite-infiltrated minerals that pretended to be fluorescent
roeblingite, bustamite, and even manganaxinite. The BIP gives
away the impostor in the latter two cases, if BIP is even a
consistently reliable indicator. (Side note: I'm still not clear
on whether roeblingite gets its fluorescence from calcite anyway.
I have seen non-fluorescent roeblingite at least once.)
Pictured specimen is about 2 3/4 inches across maximum dimension.
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