Like most gemstones, sapphire is doubly refractive and like many doubly refractive stones, it generally shows pleochroism.
Pleochroism is an optical phenomenon that is a direct result of double refraction…when a light beam splits and travels in different directions at different speeds, each component of that split beam will absorb different colors. Thus, the gem will appear to have different colors. Pleochroic gems show different colors when viewed from different crystal directions.
Blue sapphire in particular shows moderate to strong pleochroism of violetish blue and greenish blue. The photo of the ring above is a terrific example of how sapphire can show pleochroism. Pleochroism is sometimes mistaken for color zoning (another common characteristic of sapphire). For more information about both pleochroism and color zoning, visit my previous posts below:
http://www.gemologytidbits.com/blog/2011/03/28/pleochroic-aquamarine/
http://www.gemologytidbits.com/blog/2011/03/29/pleochroism-vs-color-zoning/
Author: Michelle M. Rahm is a GIA-trained Graduate Gemologist and is President of Colorado’s Mile High Chapter of the GIA Alumni Association. She has been selling gemstones and jewelry online since 1997. Visit her websites JewelryImpressions.com and OurCustomWeddingRings.com
