Under the scope a trail of round bubbles can be seen. Aha!
Definitive: synthetic. But wait a moment. I don't see curved growth
lines. (That doesn't mean they're not there, just I don't see 'em).
What puzzles me particularly are half a dozen black speck
inclusions, tiny, approximately cube shaped, at random in the
Most of the indicators suggest synthetic, but I'm not aware of
synthetics with black-speck inclusions.
Hi again Hans. To this point, your is complete, but
curved striae are only present in flame fusion and Czochralski, or
"pulling" method synthetics. But flux- and hydrothermal grown
corundum can definitely have round or elongated gas bubbles, as well
as black platinum platelets as inclusions. Most often, they contain
flux "veils" that closely resemble the fingerprints of natural
corundum to the untrained eye. These can also look like bubbles. One
of the main differences between flux veils and fingerprints is that
flux has a somewhat higher relief under darkfield illumination, which
takes a practiced eye to separate. The reason we see mostly flame
fusion synthetics these days is because the method is much less
sxpensive than the older "solution" methods. There's another
indicator; the stone has an older cut, it may be an older synthetic
You mentioned that under the microscope, you saw a trail of round
bubbles. If the trail is straight, and especially if there are
several trails occuring side-by-side, it may be a flux inclusion
referred to as "rain." If they have high relief compared to a natural
fingerprint, that's a strong indication of a flux-grown synthetic.
In short, there's no way for me to know whether your customer's
stone is or isn't synthetic without a close examination. One point,
though; if the black specks are actually cube-shaped and not
hexagonal platelets (flat and planar), it may well be a natural
stone. I've never seen a synthetic corundum with cube-shaped crystal
inclusions, but I have seen a photo of a synthetic sapphire with a
tiny ruby inclusion caused by a small concentration of chromium salts
that the sapphire captured during manufacture, so anything can
happen.. Then again, I haven't seen everything in the world...yet.
James S. Duncan, G.G.
James in SoFL