[Rockhounds] fossils

[DonH]

Kreigh Tomaszewski wrote:
>
> If fluorescence is that useful, why isn't it in all the field guides?


Several reasons.  Fluorescence is a variable property in many minerals, 
so it is difficult to catalog all the possible responses.  Difficult 
does not mean impossible, however.

Mineralogists generally scoff at fluorescence as an indicator, I have 
found, because it is inconsistent and semi-quantitative.  Textbooks 
barely mention it at all.  In grad school, I was the only one with a fl. 
light.  Even when I did a demonstration in forensics class, some of the 
students grunted with acknowledgment that it was somewhat neat, but most 
of them wore that disaffected Gen-X expression that implied they were 
too cool to look at vividly colored minerals in the dark.  There are a 
few mineralogists, such as Fred Pough (R.I.P.) and Pete Dunn, who have 
appreciated fluorescence, but most don't.

When a mineralogist describes a new mineral, they are required to report 
a number of characteristics about the species, but fl. is optional and 
is rarely reported in detail.  Therefore the trend has not been set.

The portable fl. lights of decades past were not very good.  That 
changed with the introduction of the SuperBright series in the 1990s. 
Others followed.  Now collectors can see fluorescence very clearly and 
also see it in minerals they didn't know fluoresced.  However, in the 
"old days" when many field guides were written, it may not have been 
considered that important a property.

In line with the preceding paragraph, based on the new products 
available, we now have easy access to not only shortwave (~2537 Å) and 
longwave (~3510 Å), but "midrange" (~3120 Å) and "near-violet longwave" 
(~3680 Å).  This has opened up new information about what minerals fl. 
and under which region of light.  If you have all 4 of these lamp types 
available, you can determine much more about the minerals.

There is indeed an issue with how colors are described.  The dirty 
secret of Franklin material is that, while "red and green" rolls off the 
tongue and seems quite Christmasy, the fl. color of the calcite is 
actually orange-red.  The color of Mysore corundum is actually red, and 
in fact the spectrophotometer shows that is fluoresces into the near 
infrared.  Esperite is usually described as yellow but the spectrum is 
really yellow-green.  And if esperite is yellow, then what color is 
Canadian meionite?  They are both described as yellow, but they have 
quite different spectra and look very different when lit up side-by-side.

Going back to the variability, it can get absurd.  Nearly pure calcite 
and fluorite do not fluoresce at all, but with the right combination and 
proportions of trace elements they can fluoresce in a variety of colors. 
  Again, this is not a show-stopper, but it must be recognized as a 
challenge and handled accordingly.

While I was typing this, another member sent a note talking about the 
MSH minerals.  I am moderately certain that the details of MSH 
fluorescence were the work of one man, the charming and enthusiastic 
Jacques Poulin.  We communicated on this issue several times in the last 
decade, and it took quite a bit of effort on his part to complete the 
task.  And that's the lesson: for a useful listing to be compiled, it 
takes the dedication of collectors who will gather the known minerals of 
a particular locality and catalog the fl. responses under 4 good lights 
emitting the aforementioned wavelengths.

I hope these random thoughts on the matter clarify some things.


best,
Don