Blue Spinel vs Blue Spinel.

[Bron357]

Sometimes I stop “playing with the rubies” and have a look at something else.
I have these two, very similar looking gems. While a proper gemmologist doesn’t use a Presidum gem tester, when you have dumped all your “gems” in with CZ, Crystals and whathaveyous you need a quick way of sorting the “wheat from the chaff”.
So yes, visually these two look very similiar, both test as a thermal conductivity of Spinel.
Under the microscope one has a number of interesting inclusions, the other, virtually flawless.
And one “glows” like ruby under UV the other, zip.
More research and testing now needed but it would seem to be that the one on the left is natural Blue Spinel coloured by Cobalt and iron, but the iron suppresses the UV reaction, while the one on the right is synthetic and coloured by Cobalt as synthetic Spinel is.
So lots to learn, more researching fun ahead - gems are not only beautiful but interesting.

 

[MissyBeaucoup]

It's fascinating that the iron suppresses the UV reaction. I have noticed that in some of my own gemstones. There's so much to learn that keeps it all very interesting!

I also found a website that goes into the magnetic response of various gemstones. That might be a way to distinguish some of yours, since they're mostly not set. gemstonemagnetism.com

 

[Bron357]

Yes, I read that too, but apparently there can be inconsistent magnet reactions (and I think I need a better magnet than a fridge magnet ha ha).
I’m not so good yet with the RI readings, whole concept is tricky, I can’t seem to get myself a consistent ie accurate viewing angle (grr) practice practice practice I guess, though the difference is not huge. And on the spectroscope I’m a beginner as well, practice, practice.
At least with a microscope if there’s something to see, I can see it.

 

[voce]

Fascinating...
Bron, do you know if there are there blue spinels that are colored by chromium instead of iron or cobalt? Or would that result in a red stone, not a blue?

 

[Bron357]

Fascinating...
Bron, do you know if there are there blue spinels that are colored by chromium instead of iron or cobalt? Or would that result in a red stone, not a blue?

As far as I’ve learnt so far, there’s “cobalt blue” spinels from Vietnam (which are very desirable) and the synthetic ones are likewise coloured with Cobalt - both fluoresce pink /red under LW UV (I don’t have SW UV, that’s more specialized, expensive and dangerous equipment - you need googles for SW) and Blue ones with a higher iron content that don’t fluoresce but it’s still the trace amount of Cobalt that gives the nice blue colour.
It’s the red (pink and orange) spinels that are coloured by Chromium that gives the red glow. I believe the Mahange Spinels with their neon glow are like Burmese rubies - lots of Chromium.
But then you learn in Emeralds that chromium (and vanadium) are responsible for green!
Which then leads onto Chelsea Filters introduced to ID emerald, except ones coloured by vanadium don’t show as red. They had to change “the rules” re green emeralds as some don’t show red red under the Chelsea filter.

 

[ringo865]

You can get an "earth" magnet (neodymium) for a few dollars. I got mine at kjmagnetics.com