As I mentioned previously, there are three basic gemstone types in terms of clarity:
Type I stones are usually eye-clean…those include aquamarine, green tourmaline, blue zircon and others
Type II stones generally show SOME eye-visible inclusions. Those include alexandrite, sapphire, ruby, andalusite and others
Type III stones are almost always included, such as emerald.
Sapphires are Type II stones so they generally shows some eye-visible inclusions, but they usually have a higher clarity than rubies. The enlarged picture shown above shows some fine rutile needle inclusions known as “silk” inside of this sapphire. The fine silk in sapphire is actually a desired clarity characteristic that can make a sapphire look velvety…this is especially common in Kashmire sapphires.
When the needles have a negative effect on the beauty of a sapphire, heat treatment is sometimes used to destroy rutile needles and improve clarity.
Image: Provided by GIA
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