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Steely Blue Sapphire... treated or not?


Hi everybody!
My name is Luca. I am new in gemology. I started studying the elearning course offered by IGS.
I would like to know your opinions about some steely blue sapphires from Tanzania. I bought them online and the seller declared these gems are completely natural, without any heat enhancement. The smaller stones were mounted on a bar-shaped earrings. I examined one of these stones under microscope (x100, but it was a biological microscope - I am a doctor- and I have still to buy a stereomicroscope for gemology).
Anyhow, here the images (the first one is the gem mounted on the earring, the second one is the gem under microscope:

The image under magnification seems to my inexperienced eye a rutil silk spider web! This should mean that no heat treatment has been used.
What do you think about this?Thank you for your replies!!!



It’s a little difficult to tell from your photos for certain, but what I’m seeing does not, to my eye, appear to be silk. Silk intersects at 60 degree angles, per the hexagonal growth of sapphire crystals. If you look carefully at your “spiderweb” these lines almost universally follow the girdle around the stone–varying in their angles of intersection–as more facets are present in a tier around the stone. I think these lines may represent polishing marks on the surface of the facets themselves–in other words, little grooves on the facets. Although I could be wrong.

It is important to note however, that while the presence of intact silk suggests unheated status, it is not a guaranty. Stones may be heated under lower temperatures that do not entirely disrupt rutile needles.

I’m sure a gemologist could direct you better.

Best Regards,

Dave Dawson


Thank you, Dave. I though a lot about your considerations and I think you are right: the lines are probably due to polishing marks.
Might you be so kind to take a look also to this pic?
The feature on the left side of the pic seems to me like “fingerprints”. However, I read that fingerprints may be difficult to discriminate from bubbles.
What do you think about this?
Thank you for your precious advice!


As a matter of fact, the last pic that I posted resembles me this one found on gemology-project:


Hi Luca,

It’s a bit difficult to tell from the photo, but it could certainly be a fingerprint/veil. I’m not sure what kind of doctor you are, but do you have access to an optometrist’s/ophthalmologist’s slit lamp? I’m an optometrist, and I use my slit lamp like a binocular gem microscope. Most slit lamps allow magnification from about 10x to 40x.

I’m not sure how small/large the stones are on this piece of jewelry, but it is certainly possible that these are all natural stones–unheated is less likely, but also certainly possible.




Thank you so much, Dave.
I am a Radiologist, so I do not have access to a slit-lamp.
I use my “old” biological microscope, but I am next to buy a more suitable stereomicroscope!