Color Change Gems

Color change is a fascinating phenomenon in gems.  I have seen strong color change phenomena in three stones: alexandrite, garnet and sapphire.  But there are others, such as diaspore (which I don’t think I’ve ever seen).  There are also gems that have weaker color shifting effects, depending on the angle of the light.  This is called pleochroism.  Tanzanite, tourmaline, iolite and andalusite are examples. 

Alexandrite, garnet and sapphire, can exhibit a very strong and complete change to an entirely different color in incandescent light, whereas tanzanite, for instance, especially the unheated kind, just looks different from various angles in the same light.  Depending on the gem, it can have blue, green yellow, purple and pink hues. 

Alexandrite is of course the most well known of all the color changers.  It’s also the most expensive, with a nice 1 carat piece starting at around $5000 per carat, wholesale.  Brazilian alexandrite, in my experience, often has a better color changing effect than alex from other places, changing from a strong green with teal hues to a reddish purple.  It also has a more teal(ish) daytime color, whereas Indian and African alexandrite can often be more yellow.  Historically, it is said that alexandrite changes from green to red, but I have never seen that kind of effect.  Perhaps some old Russian specimens that have since disappeared were like that.  The more affordable alexandrite usually has less of a color change effect, with the better shifting stones often looking murky and dark.  If you see a clean and sparkly gem that also has strong color change, chances are you are looking at a lab grown specimen.




My Alexandrite Parcel in Daylight





My Alexandrite Parcel in Incandescent Light

Color change sapphire usually changes from purple to pink, or from blueish purple to more reddish purple.  The effect is less striking than in alexandrite because the colors are fairly close to one another on the color spectrum.  I also own a little grey blue to reddish purple color changer from Sri Lanka.  Those are less common.  More often, you find color change phenomena in African stones, in particular, in the dark colored gems from Madagascar.  Again, the deeper the color of the stone, the more striking is the color changing effect.  Clean and brilliant stones with strong color change are not as common.  Right now, sapphire is enjoying some steep price increases, but a 1 carat Madagascan color changer is nowhere near as expensive as a 1 carat Alex (think maybe $300 per carat wholesale).



Some of my Madagascan Color Changers



Same Parcel in Incandescent Light



My Ceylon Color Changer

Ceylon in Incandescent Light

Color changing garnet is relatively new on the market, and it comes mostly from Africa, with the nicest specimens right now originating in Tanzania.  I’ve seen two kinds of color change in garnet.  There’s a brown-pink color changer, this one is much less expensive, and the effect is not always that strong.  And very recently, I’ve seen blue-purple, green-purple and reddish brown-purple effects, mostly coming from Tanzania but also from Madagascar.  Right now, these color changers are my personal favorites (although I still love love sapphire).  While on average, the effect can be a tad weaker than in Alexandrite, this is not uniformly the case.  There are some specimens with very strong color change effects.  They are also less expensive than alex right now, even though, best I can tell, they are actually more rare.  Lastly, garnet is a much cleaner stone with better brilliance than alexandrite.  The per carat price on these varies, but for a nice 1 carat piece it may be $500, for the smaller pieces it’s around $200-300 per carat.



Tanzanian Color Change Garnet Parcel

Tanzanian Color Change Garnet Parcel

In terms of treatment, all three color changers are nearly on a par.  Alexandrite is never treated.  Garnet does not respond to treatment either.  Sapphires are often heated, but for reasons that are opaque to me at this point, the color changers usually aren’t.  Perhaps the heat treatment affects the color change phenomenon, or only the nicer deeper colors change in the first place, so no heat is required.