[Rockhounds] fossils[ history of luminescent identification?]

[DonH]

jb wrote:

> That probably would be Wilkerson (The Minerals of Franklin and Sterling 
> Hill, New Jersey by Albert S Wilkerson, New Jersey Geological Survey, 
> Bulletin 65, 1962) who cites Felix Mutsche' s list (Mutsche, Felix E., 
> Rocks and Minerals, Sept-Oct, No. 242, pp. 482-485, 1954).
> 
> The earliest citation I can find from Palache ... Interestingly, he makes no mention
> of the properties in the main text  of the paper.  Apparently it was 
> thought by him to be more of a curiosity than anything else.

Back then, the phenomenon of fluorescence wasn't well-studied and 
well-documented; and also, as mentioned, really good UV lights weren't 
available back then; the iron arc was the way to go. Also, the minerals 
of the F/SH district were so fascinating that fl. was just one of the 
things that kept Palache's attention.

> The interesting thing about these studies is the use of the iron arc to 
> identify luminescent minerals. Does anyone know when this was first 
> noticed? 

According to the stories, it was noticed when the sparking of equipment, 
such as knife switches for lighting and the sparking of the wheels of 
ore carts as they crossed the gaps in the rails, caused the willemite to 
phosphoresce in the dark.  Things progressed from there.  Earl knows 
that story better than I do.

Also, fluorite from the Rogerly Mine in England will fl. in daylight, 
and that discovery has much to do with the history of fl. as a mineral 
characteristic.

> So when and where did this idea of mineral identification by 
> luminescence come about?
> What minerals, if any, are known to have been discovered exclusively by 
> their fluorescence?
> 
> Is fluorescence so common as to be confusing, rather than systematic, a 
> la Dana and others?
> Or is it so rare as to be little more than a curiosity to the casual 
> user of field guides, most of whom are out and about in the daytime anyway?

What puzzles me is the narrow focus on the generality vs. specificity of 
this property, when all determinative properties should be scrutinized 
the same manner.  For example, when I was editing the mineral ID DVD for 
a textbook, I noticed that plenty of minerals had a hardness between 6 
and 8, a white streak, and could occur in several colors.  Just as 
fluorite and calcite can have may fl. colors, they can also have many 
daylight colors, for example.  Many field guides were written when 
mineral collecting was a less sophisticated venture than now; I would 
submit that, for the more aggressive and advanced collectors, the 
classic field guides have little use.  There are well over 4,000 species 
and thousands more recognized varieties, and only a modest percentage of 
them can be positively ID'ed in the field.  When you have a species like 
members of the apatite or the biotite group that require a number of 
advanced lab tests to identify, there is little chance someone is going 
to ID the species in the field using determinative methods.  I always 
crack up laughing when I'm at a mineral show or symposium and some 
individual will look at a specimen, hitch up their pants, rub their 
chin, squint, and loudly declare that it is such-and-such mineral, a 
species that normally requires a battery of exotic tests to ID.

In a typical geology curriculum, the students taking 101 lab are given a 
tray of minerals and a guide of characteristics for identifying them. 
While some of them are similar in the eyes of a beginner--like 
muscovite, biotite, and chlorite--they all have unique characteristics 
if you apply the various tests at hand.

When we taught mineralogy, the first lab involved a re-visitation of the 
exercise from 101.  Then, the students were asked to ID some additional 
minerals, some of which had the same determinative characteristics. 
After that they were introduced to grain mounts and refractive indices. 
  Of course, two of the minerals had the same general basic optical 
characteristics, so the next week they were introduced to positive and 
negative optical indicatrices.  In other words, they had to perform 
successive iterations of more and more detailed tests, following a 
process of elimination to narrow down the ID.

Some minerals are so unique that they can be instantly sight-IDed.  Some 
can be confirmed with a few simple tests.  Others require a number of 
complementary and more complex tests.

Fluorescence is just another determinative characteristic to aid in 
mineral ID; no more or less useful than hardness or streak or color... 
You need to have a number of tools in your toolkit, and know the 
benefits and limitations of each.

Don