My best Laurellite under florescent light. (5.69 carats)This gemstone is a Laurellite. It demonstrates a reverse Alexandrite color change. It contains copper and comes from Mozambique.
Small oval Laurellite under florescent light. (5.39 carats)This 27.13 carat oval has a significant amount of veils and inclusions, but it is still flashy and very rare in its size, color and color changing properties. (Laurellite)
Large oval Laurellite under florescent light. (27.13 carats)
I have a tray of stones home because I am writing posts about them. This is a break from that work to talk about a small group of gemstones that I call Laurellite * and the gray day of August 18, 2013. Two of the stones which I will post above have been tested and reported on by the GIA. The smaller oval gemstone goes from all bluish under today’s conditions of a gray morning light with the possibility of rain for daylight, to a gray under incandescent light in a yellowish shade. I am surprised that I did not see any purplish cast in natural light. I just observed the emerald cut, which was without a purplish cast under the same morning light, but which went all the way to the most greenish hue I have ever seen, under the yellowish incandescent light Again, like the small oval there was no purplish cast in the stone, in today’s morning natural light. Now comes the one that makes it all the more interesting. I have a large ova, that is next to my emerald cut Laurellite (my best confirmed color changer ) in the tray, which stayed purplish under the gray morning light. It goes all bluish under the yellow incandescent light . Now in an evening light,which is still over cast and bluish, I am seeing purple in all these stones.
To sum up I have three color changing gemstones.
#1 Large oval stays purplish while the emerald cut and smaller oval are without purple due to the illuminant being a gray morning light.
#2 Large oval goes bluish under yellow incandescent light while the emerald cut goes to greenish and the small oval goes grayish.
#3 All gemstones have a purplish cast under gray evening sky. I can not see a great deal of difference in the sky, all day today.
(An important moral of this story is that you have to be very careful when you talk about what color some gemstones are under “natural” light, because “natural” light is not a constant illuminant. Color changers are defined using idealized artificial illuminants.)
I wish I knew why the change in color is different. The smaller stones have been test by a couple of labs and found to contain about the same concentration of copper with the oval having much more manganese than the emerald cut. I have never had the large oval tested. I doubt that I will ever know more details, since Laurellite is so rare and what there is of it, is being heat treated to the cyan blue that can be claimed to be paraiba-type tourmaline and command a big price tag. More to come in other posts.
* Laurellite is a name I have given to copper bearing tourmaline from Mozambique the exhibits a reverse Alexandrite color change. It changes from a violet in some natural light and to blue/green, blue to gray in yellowish incandescent light. This reverse Alexandrite color change is unique in the gem world. It has been confirmed by the GIA as a new variety of Elbaite and written up in their Gems and Gemology Magazine.