FMF - Friends of Minerals Forum, discussion and message board

[Tom Tucker]

I don't think I've seen it added to this list of light sensitive mineral species - the NONTRONITE crystals from the syenite in Stoutameyer Branch, Augusta County, Virginia, is very light sensitive. Micro-crystals exposed to the light under a 'scope will turn from very light grey to dark grey or black within 12 hours of any light exposure.
John got more snow than we did in Virginia, Tom

[GneissWare]

[Amir Akhavan]

John, really a funny experiment, but the poor South-American amethyst is not used to snow.
Don't you feel sorry for leaving it out in the cold winter nights while you sit by the fireside?

Smoky quartz is sensitive, but I've seen crystals laying in the sun at 2800m altitude for years that did not pale. It's difficult to say why supposedly same color centers fade more quickly in some specimens than in others.

Anyway, just as Alfredo pointed out, rose quartz is completely insensitive to light.
Those pink crystals with phosphorus color centers that some call rose quartz -but I don't- are very sensitive to light.

[John S. White]

Amir:

I have been thinking of taking the piece of amethyst with me to Tucson for two weeks in the desert sun. It might like a vacation from the cold, just as we do.

And it might also enjoy reuniting with thousands of its relatives while there.

[Elise]

I am following this thread as it coalesces so that I might add the information back into my copy of Frank Howie's book. One aspect I am wondering about is the type of lighting and the type of display -- that is, glass vs polycarbonate and their interaction with different lighting in regards to sensitivity of the specimens (with light directed from outside a case). In the chapter by Kurt Nassau, there is a comparison of amount of damage from UV: sunlight > sunlight though glass > UV absorbing plexiglass > florescent lights > Incandescent light. Also, some cabinets with interior fiberoptic lighting mitigate the heat, but what are the implications for light sensitivity? (based on different light sources which are remotely located- from what I have seen the source is in the base of the cabinet - Jordi posted a picture recently of a nice one at Tucson, I don't know if the lights were fiberoptic in that one, but looked similar).

Not so much related to the sensitivity, but rather to viewing, I was shocked to look through a polycarbonate transparent desktop with a dichroscope -- started considering what the color change of objects viewed through such a material would be. It gets very complicated!

And because I can't resist:

[John S. White]

Elise:

I will jump in here and simply say that it has been many, many years since I have seen the book by Herbert Zim so I cannot recall what my impression of it was. I don't believe that is was negative but that is just a guess at this point in time.

[Elise]

Going back to Matt's synopses from Frank Howie's book posted earlier in which he points out the classifications Dr. Nassau used:

a). light induced colour changes.
b.) light induced decompositions
c.) light accelerated surface reactions with air, moisture and pollutants

Could the shortened and revised "A" list being generated be divided into the categories above, or at least notated as such in the new list?

Re: "Goldens" as I said, I couldn't resist and penned with a smile. I think many people of science today have fond memories of those books from their youth and it is noteworthy that many still have them on their shelves. Most assuredly the poster's point was that references should be reliable (and cross-checked); I should not have blurred his caveat with a digression.

The Howie book was published in 1992 (with a reprinting in 2002, not revised). In the foreword C.G. Cruchy states "I have no doubt that some of the ideas expressed in this work will change over time; in fact I am sure that the authors, and others, have already begun the research that will change our present views during the next few decades." We already know that causation of color for some materials has only been recently worked out or in some cases revised in the last 18 years, so efforts on developing a revised list are very welcome, especially as overseen by the members of this forum. (additionally, the development of new lighting systems adds to the mix, re my earlier inquiry).

All the best,
Elise

[John S. White]

We are now counting down to six months of my amethyst being outside (note that I am not claiming it was in the sun for six months, there were numerous cloudy days and while I was in Tucson we got about 3 feet of snow, so it was weeks before it was exposed again). In any case I have photographed it again next to the control sample which has been kept inside in a dark area. These two pieces were once attached. The one that was outside is on the left. It hasn't lost any of its color yet.

[John S. White]

New update to come in the saga of the amethyst, watch for it! Today marks 8 months in the sun (sort of). Very interesting results.

[John S. White]

As promised, an update on my experiment in which a specimen of Brazilian amethyst has been placed out in the elements for 8 months now while its former neighbor has been protected from direct light indoors for the same period as a control.

In the photo, the piece on the left is the one that has been outside, that on the right inside. One can easily see that the piece on the left is noticeably lighter than the other one. BUT, does this mean that the amethyst has faded? Surprisingly I believe it does not. The piece on the right has a distinct smoky component which makes it appear darker than the one on the left. The one on the left has lost the smoky component as a result of its exposure to ultraviolet light, a result that I certainly did not anticipate.

Big surprise for me, I hope others find it interesting as well.

[Jordi Fabre]

Fascinating. Maybe some relationship with the radioactivity related with the smoky Quartz? If true that they become smoky in ambiances with radioactivity, maybe the sunlight with its small charge of radiations can turn back the process?

[Jim Prentiss]

Hi everyone,

There is a lot of good information on this forum, but has anyone actually created a "list" of sensitive minerals for reference?

Just thought I'd toss that out.

See ya later,

Jim Prentiss

[Antonio Alcaide]

Hi everyone,

I'm afraid I accepted the responsability of writing the list. I am collecting all the information not only from this thread but also from the Spanish side and from articles and books. I work very slowly, so I must apologize for that. Especially due to my tasks in the Spanish Message Board and my own inappropiate background. I have a rough draft, but I want it to be a practical one, it is to say, far away from a theoretical list with species without have been contrasted. All ideas are welcome.

PS: Jim, I do not understand very well your words: "toss that out". Do you mean to rule it out, not to consider it at all?

Regards

[Jim Prentiss]

Hi Antonio,

Thanks, I did not know anyone was actually doing a list.

It is an Americanism for bringing it to the attention of the group. By no means toss it out I am eagerly awaiting the list.

See ya later,

Jim Prentiss

[Antonio Alcaide]

Hi again Jim,

Now I feel encouraged by your words -especially with your kind explanation- and the list will appear soon.

Thanks for your daily patience with us, those who do not speak English as our first language. It is easy to speak broken English but almost impossible to have a good command of it.

Cheers