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GeneralCorundum

10th Mar 2015 09:25 UTCAnonymous User

Hi, I bought a new specimen from a reliable seller in eBay, it is labelled Sapphire/Ruby, but it has purple-blue colour. So I named it as Sapphire in my Mineral Documentations. But when I put it under UV light, the crystal turns bright red. Based in my basic knowledge in Minerals, Sapphire is not fluorescent at all, but this one does, and its red. So I suspect it to be synthetic (I hope not).

I hope someone here can enlighten me.

Thank you.

10th Mar 2015 11:37 UTCJosé Zendrera 🌟 Manager

A picture will help us to clarify this issue.

Some corundum specimens have both red (chromium) and blue (iron) chromophores giving a violet/purple color, that is what could happen here. In these cases ruby fluorescence can prevail when iron content is low.

Synthetic corundum usually do not have solid inclusions, maybe you can check this with a loupe or microscope.

10th Mar 2015 12:50 UTCOwen Melfyn Lewis

Joshua,

Strong fluorescence and the presence of an appreciable amount of Fe are never found together. Fluorescence in mined ruby can vary strong to inert and still be ruby by colour (rather dark).

Neither crystal form nor the absence of inclusions is proof that a specimen is not of synthetic origin only it has probably not made by the flame fusion process.

A picture of the specimen would be helpful. You have not even said whether it has a crystal form, is broken rough or of a cut and polished stone. So, for the moment, there is no sensible advice that can be given - except look closer; test and report more.

One tip. If the stone has been faceted and polished, be sure you photograph it face down on a diffused light source (small torch covered by a white handkerchief will do in an emergency). The camera needs to be vertical relative to the plane on which the stone is resting. This is not a glamorous view but if the image is SHARP will show details that cannot be seen in other views.

10th Mar 2015 23:58 UTCAnonymous User

Thank you for your responses sirs, your inputs are helpful, I will post the images after I acquire some later this week.

14th Mar 2015 07:43 UTCAnonymous User

Here's the photo's, please check it out.

14th Mar 2015 16:50 UTCOwen Melfyn Lewis

It's not possible, for me at least, to relate the two images you show. Nothing you show indicates any possibility at all of synthetic growth. You do not give the wavelength of the UV source you were using or indicate to what part of the daylight image the red fluorescence relates. Do you have a source locality for the specimen?

The blue crystal shows, on the top face - a perfect cleavage? - a pronounced pattern of parallel lines intersecting at close to 90 deg. So not corundum, I think. Kyanite might be a possibility? Are you able to check the pleochroism?

14th Mar 2015 18:50 UTCDoug Daniels

I agree with Owen - the two photos don't match. And, neither suggests corundum; well, the first might, but it is only showing the fluorescence, but not the daylight view - could as well be calcite.

The patterns on the blue crystal, certainly not like any I've seen on corundum. As always, where did the specimen come from (its locality)? That is important.

16th Mar 2015 11:07 UTCPeter Slootweg 🌟

Hi Joshua,

Do not worry about this specimen. It is a real corundum crystal. The patterns on the crystal faces are very distinctive of this material, the lines intersecting at 90 degrees are due to twinning. The pits are a result of the fact that it grew in a restricted enviroment as most corundum does. The fact that is fluoreses does not mean it is not real. This material is often a mix of red and blue zones. if the reddish zones fluores strongly it will make the complete crystal lit up. The matrix of biotite, feldspar and garnet with this type of corundum is typical for the Zazafotsy quarry in Madagascar where i think your specimen originate.

Peter

16th Mar 2015 13:50 UTCAlfredo Petrov Manager

I agree with Peter:

probably Zazafotsy (or some nearby locality)

The matrix in the second photo is classic, and impossible to synthesize.

But, like Owen, I cannot see how the first photo relates to the second. If you take both UV and daylight photos, it would be much more useful to take them from the same angle.

16th Mar 2015 14:06 UTCOwen Melfyn Lewis

Peter,

Lamellar twinning in corundum - certainly. But not in two directions at 90 deg to each other, surely? Indication of a 'top surface' cleavage plane? Your comment on possible locality and association with feldspar is very interesting as such 90 deg cross-hatching (cleavage) is not uncommon in feldspar (esp. orthoclase). Like Doug, I have never seen it in corundum

I wonder if we are being misled by the red fluorescence? I cannot relate the fluorescent shape to that of the blue crystal. Are the two one and the same? Further explanation with more images from Joshua might help. (Ed: Crossed with Alfredo's post above).

16th Mar 2015 15:55 UTCReiner Mielke Expert

Hello Owen,

Maybe that is not a cleavage face but an irregular prism face and what you are seeing at 90 degrees is the same as this: http://www.mindat.org/photo-305989.html

16th Mar 2015 16:00 UTCOwen Melfyn Lewis

Thanks Reiner. That weighs heavy in the scales :-)

16th Mar 2015 16:04 UTCPeter Slootweg 🌟

Hi Owen,

Regarding the 90 degree crossing lines, these are parallell tot the rhombohedral unit cell. Yes, they are not exactly 90 degrees but it looks like this in the picture. If you orientate a calcite cleavage rhobohedron in the right direction and look at it with one eye it would appear square as well. You are looking at one of the prism faces and to my experience this type of striations on corundum is very common, if not tell tale. Feldspar does have cleavages in multiple directions but not in this orientation.

I'm not sure what you mean by "Top surface cleavage plane". The cleavages run all the way through the crystal and are natural weak spots in the crystal lattice therefore they will be exposed upon the slighttest etching or reabsorbtion. http://www.mindat.org/photo-493506.html is a example from the same locality. The upper crystal also shows these intersecting lines.

I hope it explaines my point of view.

Kind regards, Peter

16th Mar 2015 16:26 UTCOwen Melfyn Lewis

Thanks, Peter.

18th Mar 2015 02:45 UTCAnonymous User

Oh! I'm so sorry about the image! I uploaded the wrong photo, I didn't check it. I'm so sorry for the late response too. The second one is my specimen, the first one is another corundum with the same locality. My specimen florescent exactly like the first photo and yes it's from Zazafotsy quarry in Madagascar. I believe the matrix is Schist (not sure). Anyway, your info's added my knowledge in Corundum, as a beginner I'm still quite confused about the terminologies, but I'll get there.

Thank you all for your time and inputs sir José, sir Owen, sir Doug, sir Peter, sir Alfredo, sir Reiner, much appreciated.

18th Mar 2015 15:33 UTCOlivier Langelier

A nice little sapphire indeed

19th Mar 2015 01:40 UTCAnonymous User

It is, thank you Olivier.

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