2007-03-26

fluorescent minerals



I had an opportunity to travel to Philadelphia at the end of last week on business, and I found it an opportune time to travel north a bit on Saturday to Franklin, New Jersey to one of my favorite places . . . the Franklin Mineral Museum and the fluorescent mineral collecting site directly behind the museum. This was my fourth trip to Franklin and I enjoy it more each time. I was looking for flourescent minerals and I sure found a load of them on Saturday. I just happened to be there on the first day of the collecting season. A week earlier and I would have found the site under snow.

The first rock that I spotted looked different to me. I didn't recall having seen one like it there before, so I held on to it and kept moving it to the top of my bucket each time I placed another rock in the pile to be sorted. My first rock turned out to be a combination of willemite, zincite and franklinite. When I placed it under the short-wave UV light, it fluoresced a bright blue. It is really stunning. I also found several red willemite and several green willemite specimens. I found a piece or two of barite, there were several specimens with just a tinge of yellow fluorescence and one or two with specs of beige. And of course, there was "tons" of calcite brilliantly glowing orange. I have always found the combination of calcite and franklinite to be an attractive-looking specimen. The pictures above are red willemite from my Franklin excursion. The top one in under fluorescent light. The bottom one is under short-wave UV light.

Now just a few words about fluorescence.
Fluorescence is a property not found in all minerals. Minerals that do fluoresce, glow when exposed to either short-wave or long-wave ultraviolet light. Examples of fluorescent minerals are autinite, calcite, diamond, eucryptite, fluorite, hyalite, scheelite and willemite. Minerals from the Franklin and Sterling Hill area of New Jersey are known for their fluorescence. There are over 80 fluorescent minerals found in that area. Franklin/Sterling Hill fluorescent specimens usually contain 2-4 minerals in a typical specimen though some have up to 7 fluorescent minerals found together.

Fluorescent minerals contain particles in their structure which respond to ultraviolet light by giving off a visible glow. Ultraviolet light is a form of electromagnetic radiation invisible to the human eye. It is given off by the sun and by common fluorescent lamps used for lighting, but they also give off considerable white light (visible light), preventing the fluorescence from being seen. The ultraviolet reaction is visible with a special fluorescent lamp with a filter that blocks white light but allows ultraviolet light to pass through. This lamp is known as an ultraviolet fluorescent lamp, or UV lamp. The reaction will only be visible in a dark area, where the presence of white light is weak.

There are two ultraviolet wavelengths: long-wave and short-wave. Some minerals fluoresce the same color in both wavelengths, others fluoresce in only one wavelength, and yet others fluoresce different colors in different wavelengths. Some UV lamps have two separate filters: one for long-wave and the other for short-wave. There are more minerals which fluoresce in short-wave than there are in long-wave.

Color and intensity of the fluorescence varies among specimens of a particular mineral. However, specimens from the same locality almost always fluoresce the same color. For example, calcite may fluoresce red, orange, yellow, white or green.

When a fluorescent lamp is lit, never look at the light source, as it can damage the eyes permanently. In addition, skin should not be exposed to the light source for extended periods, as it can cause sunburns and long term skin problems.

If you have a question about fluorescent minerals, if you have additional information to add to this post about fluorescent minerals, or if you have a question or comment about another subject, please click the comment link below.

5 comments:

Howard Allen said...

We oilfield geologists also use fluorescence to judge the grade or "gravity" of oil on core or chip samples recovered during drilling operations. Heavier oils (thick, tarry oil) fluoresces brown or dull orange. Lighter oils fluoresce progressively "cooler" colors, from light orange, through gold, yellow, white to bright bluish white (try a shot of WD-40 under your fluoroscope). Common long-wave UV lights are sufficient for this sort of testing.

Mike B said...

The rocks that I collected last weekend in Franklin, New Jersey arrived yesterday and I had tons of fun sorting them and looking at each one under the UV light. The specimen above is one from my Saturday adventure. It is red willemite. If you look closely in the top picture you can see the red specks throughout the piece. The black specks in the piece are franklinite, which does not fluoresce. I've added a couple of pictures to the original fluorescent post. The top picture is under normal fluorescent light. The bottom picture is under short wave ultraviolet (UV) light. It is interesting that red willemite fluoresces green.

Altogether I collected about 60 specimens Saturday. I could have brought home more, but I wanted to keep the shipping costs down to a reasonable amount. That also gives me an incentive to go back . . . again. Franklin is one of you favorite collecting sites in the country.

Anonymous said...

Hi! I have a question about a mineral that I picked up in the south of Spain. I think it's a "desert rose" but it's really big and I've never seen another one like it. Is there a way I could send a picture to see if you know what it is?

Thanks!
-Mary

argon(one) said...

If you leave a comment here, please state it in English, since that is the only language I understand. Because I cannot determine the content of a comment left in a different language, I must delete it.

Nothing personal, I just want to make sure the comments here are family-friendly. Thank you for your understanding.

Anonymous said...

Can you distinguish a pink sapphire from a pick diamond using a hand held shortwave fluroescent lamp? If so, what should I look for?