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 Post subject: Observations and revelations concerning purple tourmaline.
PostPosted: Sat Oct 08, 2016 11:49 am 
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Joined: Thu Sep 25, 2008 10:33 am
Posts: 840
Location: Mars PA
Of all the colors found in tourmaline, I think that purple/violet has one of the most interesting histories that is still unfolding today. Some of the listed observations and revelations below I have only read about and i hope that I make that clear. Other adventures I have lived.

1. I did not include violet in the title because I ran out of space. But violet and purple are very different in the physical world of color, but are associated in people's minds (blue/red). Purple is a composite color, which means that it is formed by the mixing of spectral colors. Spectral color are found in the rainbow and have a range of wavelengths associated with eye's perception of the color. With violet it is at the edge of the visible color range on the most energetic end.

2, Rubellites and pink tourmaline with a violet/purple overtone are not particularly rare. some collectors prize them as highly as a purer red and others do not. I think the name Siberite which is an old name that was derived from Siberia, covers this reddish purple family. But I have never seen a specimen in a museum labeled Siberite so I have never really seen an authentic specimen of Siberite from Siberia. (Maybe #572, tray #12 and #274, tray #6)

3, I have found more reddish tourmalines that distinctly shift to purple/violet under the bluer skies of inclement weather or other times when the daylight is "bluer", than strongly purplish/violet tourmaline under the light sources used to grade diamonds. (#292, tray #6 and #572, tray #12)

4, I have a 10 carat Nigerian Rubellite that is a rich red under "normal" daylight conditions without any discernible purplish cast, turn completely purplish under gray raining conditions at a jewelers. I had never checked the gemstone under such conditions and was quite surprised. The tourmaline I just had reported on by the GIA and written about in a recent post, turned out to be an exceptional example of a Rubellite with a higher level of purple, than most, under all daylight conditions. (#572, tray #12)

6, I do have a group of tourmaline that I consider mostly violetish and would not use the name Rubellite with them. They come from Madagascar and have a color that is really hard to describe. They are not bluish, but it is not just grays that modify its basically violet color. My best color in this group is really quite pleasant with a decent level of saturation, but it is the exception, not the rule. (#715, tray #15)

7, Bluish purple/purplish blue is the hardest color in tourmaline to get in my opinion. With this I mean a color with a distinct mixing of purple and blue. I see at least one price listing of tourmaline for violet/blue and it is stated as a common color. I have not seen this material or my eyes are not good enough to pick up the line between blue and purplish blue. I hope to get my spectrometer up and configured to test my eyesight. (#592, #582 both in tray #12)

8, Now no discussion of tourmaline's range of color in the purple/violet part of the color wheel would be complete without a look at copper as a chromophore in tourmaline. Now copper alone can not produce purples/violets and the form of the manganese ion is critical in modifying copper's cyan color to the purples/violets.

9, It is proposed by some researchers that all manganese that exists as a trace element in tourmaline was in the lower oxidation state of Mn+2 and that natural radiation oxidizes the manganese to the high oxidation state of Mn+3. This form of manganese is a much stronger chromophore and the reduction of this ion to Mn+2, by heating, is critical to the creating of most, but not all Paraiba/paraiba type gemstones.

10, I don't think that anyone knows what percentage of cuprian tourmaline are heated to form their cyan blue color. (The laboratories can not confirm whether a tourmaline has been heated or not.) The process takes place at moderate temperatures with a normal composition of gases, so it is available to just about anyone that wants to try. And in the case of Paraiba it has been reported that everything was heated. Even top quality naturally blue ones that had just a hint of gray. All the reds and purplish blues/bluish purples were certainly lost to the fire in my opinion.

11, An important point that I have seen in cuprian tourmaline from Mozambique is that the heating process has NOT always been taken to completion, with all the Mn +3 reduced to Mn +2. Partial heating can produce an excellent violet with a pastel tone level from material that was too dark purple red out of the ground. (The complete heating of the tourmaline produced a very pale aquamarine color many times.) The dark purple red color/tone value/saturate was common, at first, in the Mozambique deposit. In other words, this means that just because a tourmaline maybe cuprian and still purple, it is unheated. (#31, tray #1)

12, With the discovery of the Mozambique deposit of cuprian tourmaline, the whole wide and wonderful world of color in cuprian tourmaline was renewed or even discovered. I have never found any attempt to present a complete picture of all the colors found in Brazil so a comparison with Mozambique is really impossible for me. Still I think the purples found in Mozambique are more distinctive than its heated or unheated blues. I might go as far as to say that the amethyst like colors such as my exceptional gemstone and perhaps some other purples were never found in Brazil. It is sad that more information and testing wasn't done on unheated Brazilian material. (#291, tray #6, #487 tray #10)

13, Finally, I am sure that world of color in tourmaline, particularly the purples, would be much reduced without copper (a long with manganese) as a chromophore. The blue hues can be duplicated by iron , but it seems to be very rare for it (along with manganese) to produce purples/violets with the same saturation, color and tone values as cuprian. It is unfortunate that the fires still burn even this new generation of purple/violet tourmaline.

My disclaimer is that my attempt to briefly look at purple/violet tourmaline should not be considered complete. Please add anything relevant and enrich our understanding of a beautiful gemstone.

Bruce

All numbers along with their associated tray numbers, after a paragraph, are for my collection that can be viewed at brucefrytourmaline.com. Thank you for visiting.


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