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PhotosAmethyst - Exposed to UV / Heat

19th Aug 2015 04:48 UTCJuan Ángel Tort Figueroa

WOW!!!

19th Aug 2015 05:25 UTCDoug Daniels

Now how did they done do that?

19th Aug 2015 05:45 UTCAlfredo Petrov Manager

I suppose one could bust up the amethyst and glue the pieces back together after the experiment (as is explained in the photo caption).

Congrats to Amir - - - Amazing and educational demonstration! One experiment is worth more than hundreds of pages of theorizing and hearsay. :)-D

19th Aug 2015 16:00 UTCRob Woodside 🌟 Manager

Great work! Thanks!!!

19th Aug 2015 16:25 UTCSteve Hardinger 🌟 Expert

Now let's see the same thing done with a beryl....

19th Aug 2015 16:38 UTCErik Vercammen Expert

A picture like this should put in the head of (best-of-)articles about quartz and amethyst!

19th Aug 2015 16:51 UTCAmir C. Akhavan Expert

There's really not much to it, except for patience in the case of the UV irradiation.

If you don't have an idea of how long it takes and don't see any obvious changes after leaving the specimen a few days in the UV torture chamber, you start to have doubts about your setup.

These germicidal UV C lamps only emit a line spectrum, and it is probably more effective to use broadband UV sources, like deuterium lamps or high-pressure mercury lamps. Unfortunately, these are more difficult to handle and - in particular deuterium lamps - are very expensive. I've been thinking of adding 100W halogen lamps to boost the process, but then you need to deal with the enormous heat these lamps generate.

I forgot who it was, but some researcher in Brazil could pale specimens in just a few days with a more professional setup.

19th Aug 2015 17:40 UTCMichael Wood

Excellent demonstration and explanation Amir, this is very useful information!

Thanks! :)-D

19th Aug 2015 19:09 UTCJosé Zendrera 🌟 Manager

Bravo! A very didactic and aesthetic example of amethyst treatments!

Just for comparison, let me show an amethyst after about ten years under sunlight. 80% of color was gone after the first year and later the discoloration process slowed down progressively as noted by Amir in his torture chamber.

19th Aug 2015 19:53 UTCGeoff Van Horn Expert

Awesome! One thing I'd like to see is the top right cut in half again with one piece left as is and the other exposed to an industrial gamma ray source.

19th Aug 2015 21:37 UTCWayne Corwin

True Geoff, it needs a dark smoky section (tu)

19th Aug 2015 22:54 UTCAmir C. Akhavan Expert

An extra smoky color patch would certainly look cool, but if it hadn't been smoky already in its natural state, it's not likely that it ever will be (again).

I will do gamma irradiation "experiments", too, but this particular specimen will not be touched again, it took almost 4 months to create it, and I like the way it looks and don't want to risk destroying it.

19th Aug 2015 23:19 UTCPeter K. Szarka

An excellent presentation!

Can it be presumed the very same procedures would alter other familiar 'enhanced' minerals such as topaz, beryl and tourmaline?

20th Aug 2015 00:43 UTCOwen Melfyn Lewis

Nicely done Amir! :)-D

@PKS. It depends. The processes for all the minerals you mantion (including quartz) can undergo colour alteration by affecting one or more chromophore trace elements present in the material. The presence of these trace elements can vary from area to area and even from specimen to specimen. Some of the colour changes are stable and others are not. Amethyst to citrine is stable at normal room temperature but can be reversed by gamma irradiation. The colour of light pink or light green spodumene can be deepened by gamma irradiation but will fade again in the presence of UV in a matter of weeks or even days.

All the processes work at the atomic (not molecular) level, where energy at some given level causes some change in the atomic structure of the chromophore. Probably the most common effects are caused by making some chromophore atoms lose or gain an electron.

Some of the alterations also depend on where in the crystal structure the chromophore atoms are held. For example, in beryl Fe atoms may substitute for Al in the unit cell or the Fe may simply be 'trapped' in the 'channel' within the cyclosilicate rings. If the Fe is only present as an Al substitution, irradiation will alter the colour from colourless to yellow. If the Fe is present only as channel-trapped, irradiation turns the crystal light blue. If the Fe is present in both locations, irradiation will turn the crystal a sea-green colour (the colour most natural aquamarine). If sea-green beryl is moderately heated, the valency of the structural Fe changes back, causing the yellow colour to revert to colourless - but the channel-trapped Fe is unaffected by this heating, leaving the stone with the light blue colour that today's markets demands for aquamarine.

All quite complicated with books been written to cover the science of the various processes - and then highly conditional depending on the chromophores present. In the lab, composition of synthesised minerals can be well controlled but, working with what comes from Mother Nature's lab, produces variability in the results obtained.

20th Aug 2015 02:06 UTCGeoff Van Horn Expert

You can get a very good understanding from Kurt Nassau's book Gemstone Enhancements.

20th Aug 2015 10:05 UTCOwen Melfyn Lewis

Yes, for colour alterations caused by radiated energy in the gamma - x-ray - UV - vis -IR band there is no better cook-book. For a deeper understanding of the causes of colour and the various interactions between matter and radiated energy that cause the human perception of colour, Nassau's 'Physics and Chemistry of Color. The Fifteen causes of Color' remains the standard text-book.

20th Aug 2015 19:40 UTCPeter K. Szarka

@Owen

I appreciate the time you took to explain some of it. I always been interested in knowing what may have been done to various specimens I've come across.

@Geoff

Thanks for the lead on that publication.

21st Aug 2015 05:01 UTCRuss Rizzo Expert

Steve Hardinger Wrote:

-------------------------------------------------------

> Now let's see the same thing done with a beryl....

I recall seeing a photo back in the mid-90's (published in Minrec I believe) of Bill Larsen holding 2 halves of a monster-sized Beryl crystal from Volodarsk-Volynskii; one half was the natural yellow color and the other half treated to change it to a deep sky-blue color.

Russ

I'm positive that my cats are plotting my demise...

23rd Aug 2015 02:50 UTCRock Currier Expert

Juan,

That's a great photo, but could you please upload it formally to our database and explain in the caption what portion is what? I have done similar things in the past but not neatly as you have. The specimen is that of a amethyst on agate specimen from Artigas, Uruguay. It has clearly been broken cleanly into four sections. The upper left one is the dark amethyst which is what the other sections looked like before treatment. The lower right is obviously the portion subjected to heat treatment. What I would particularity like to know is how the other two sections were treated. In Uruguay. At the Polleri mine, they stored the light colored amethyst, that was not immediately salable, on the ground in the shade of a little grove of eucalyptus trees. This slowed down the bleaching process of the sun far more than if they had left it in the sun. There must have been an at least an acre or two covered with specimens. In the sparsely vegetated grazing land around some of the mines you could easily find agates and clusters of battered white quartz crystals that must have, at one time, a pretty amethyst color. They had weathered out of the agate and amethyst rich basalt below.

23rd Aug 2015 04:53 UTCJuan Ángel Tort Figueroa

The Great work is by Amir C. Akhavan

A part of a deeply colored amethyst geode from Rio Grande Do Sul was cut into four pieces.

Three of them were treated with heat or UV radiation. The four pieces were glued together again after treatment.

Top Left: Untreated, original color. Color seems to be evenly distributed in the tips, but is most intense 1-4 mm under the rhombohedral crystal faces.

Top Right: Exposed to UV light from two 18W low pressure mercury lamps (germicidal UV-C lamps) for 3 months. The crystals have lost almost all their color, but some slightly violet patches are still visible inside some crystals. Fading proceeds relatively quickly in the beginning, but slows down with time. The complete bleaching would probably have required another 2-3 months of exposure.

Bottom Left: Heating to about 380°C for 8 hours resulted in loss of most violet color and an overall patchy appearence. Some crystals are still colored violet in central parts while the outmost layers of the rhombohedral faces start to develop a yellow-brown color.

Bottom Right: Heating to about 450°C for 12 hours. The violet color is gone, and a orange-brown color appears that is most intense close to the surface. Note that the most intense violet color of the untreated crystals is not directly at the surface, but a few millimeters inside the crystals.

Size of specimen 138 x 81mm.

Mindat.org Photo of the Day - 19th Aug 2015

Copyright: © aca Photo ID: 700718 Uploaded by: Amir C. Akhavan View Count: 2232 Approval status: Public galleries Type: Photo - 7776 x 5024 pixels (39.1 Mpix)

10th Feb 2024 15:19 UTCCarles Millan Expert

Amazing experiment!!

23rd Aug 2015 08:50 UTCAmir C. Akhavan Expert

Hi Rock, if you are sure of Artigas, I'll change that, you know these specimens better than me.

23rd Aug 2015 09:44 UTCRock Currier Expert

Amir,

I believe it almost certainly is from the Artigas area because of the strong amethyst color, the small crystal size and thin specimen thickness. This along with the fact that the amethyst appeared to be growing on what appeares to be a solid agate matrix. I have never seen specimens like this from any Brazilian locality and and it is a dead ringer for the material produced around Artigas.

But who knows? Considering the kilotons of amethyst dug in Rio Grande do Sul each year they may have found specimens like this, but I have never seen any. Even if he bought the mineral in Rio Grande do Sul it is not likely to be from there. Much Uruguayan amethyst in imported into Brazil and sold along with the Brazilian amethyst by agate and amethyst dealers in towns like Soledade. The dealers will not often tell you exactly where the amethyst comes from unless you drill down on them and sometimes they don't even know for sure. I would say, short of Juan buying the specimen right at a locality in RGS, that the specimen is from Artigas.

23rd Aug 2015 18:36 UTCRob Woodside 🌟 Manager

I was too blown away by the colours and missed the matrix, but Rock is right, Artigas.

23rd Aug 2015 19:02 UTCAmir C. Akhavan Expert

Thanks. I'll make it "probably Artigas".

The photo isn't associated with any locality, anyway.

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