Back to IGS | FAQ | Contact

Alexandrite or Sapphire?

Is this Chrysoberyl or Corundum? The stone is Bluish Green in the Daylight and Eggplant Purple with a hint of pink in Candlelight. It weighs 12.18cts. It’s Refractive index is 1.760 and is Biaxial of 1.760 to 1.769 and 1.770 to 1.766. From my research this stone fits into the Chrysoberyl RI of 1.740-1.777 range but misses the 1.745–1.759 range for Alexandrite. It could be Corundum with the RI of 1.757-1.779 but if it’s Sapphire with the Bluish Green color shouldn’t the RI need to be 1.762 to 1.770 (+0.009 / -0.005)? I noticed that AJSGems.Com has a slightly different RI for Alexandrite of 1.746-1.763? I think this is Chrysoberyl and has the required colors for Alexandrite but slightly misses the mark on the RI for Alexandrite?
See attached photos.


Image 4 Green
Image 5 Purple
Image 6 Teal Purple

Hi Tracey.

You should make an SG (specific gravity) test on the stone. Corundum and Crysoberyll have different weight. You should also look at it through a spectroscope.

Regards
Pierre

2 Likes

Most likely color-change natural sapphire.

2 Likes

Hi. Thank You for your response. I can see from your profile that you’re a Gemologist. Can you tell me what this is, it looks cloudy and like rain in the first image. The second image looks like cloudy banding? Does this look like a color change Sapphire or a Parti-Sapphire to you? Also, do you know what the RI range is when cutting a rough Alexandrite?
Milky Cloud Rain|636x424

Milky Cloud Rain