FMF - Friends of Minerals Forum, discussion and message board

[MSrockhound]

At my local gem and mineral show this weekend I picked up two specimens of corundum labeled as being from Ilmen Mts, South Urals, Russia.

However, the sapphire appears to be on a feldspar matrix while the other is maybe quartz or dolomite? I have yet to run scratch tests as I'm nervous because they are brand new specimens so I'm not sure if the black on the ruby specimen is some hornblende, amphibole, biotite, or schorl. The matrix may not even be quartz.

My questions are as follows:

1. Is the ruby from the labeled locality? I have my suspicions its not

2. Would it be possible for ruby and sapphire to occur at the same locality, in different strata?

Theoretically yes I suppose but the likelihood of two strata of very different host rock displaying different grades of metamorphism would having both varieties of corundum seems unlikely in one area.

3. I understand there are also samples of bi-colored corundum displaying both red and blue, are those half sapphire or ruby?

4. Where might my ruby sample be from? India or Thailand?

Thank you for any and all help!

A Curious Undergrad,
Chris K.

[GneissWare]

The blue one looks right for the Ilmen locality. The ruby looks right for Mysore District, Karnataka, India locality.

[gemlover]

Yes, ruby and sapphire can occur in the same locality. Check out the geology of Franklin, NC (natural ruby and sapphire mines) then that trends NE to the Hiddenite NC area (emeralds).

john

[alex chaus]

[Peter]

The sapphire is indeed form one of the pematites in the Ilmen mountains. I do not have my litterature here but if my memore is corect this is from pegmatite 298.

The ruby is from Khit Ostrov (Khit Island) in the White Sea, Karelia, northwestern Russia, just south of the Kola Peninsula.
Best regards Peter

[Riccardo Modanesi]

Hi to everybody!
John, as an example, as you know very well, ruby and sapphire may occur not only in the same locality (i.e. plenty of mines in Madagascar, Sri Lanka etc.), but also in the SAME CRYSTAL!!! Mong Hsu rubies have a sapphire core, which is erased by heat treatment. Winza (Tanzania) corundums contain often both a red and a blue part! Then I am not astonished at all if the two crystals shown here are from the same locality.
Greetings from Italy by Riccardo.

[Roger Warin]

Hello,
Pure corundum (aluminum oxide Al2O3 formula) is completely colorless. However, it may take multiple colors from a transition metal replaces aluminum in the structure.

Ruby is red because of the presence of Chrome cations Cr3 +.
When corundum contains Fe3 + , it becomes yellow sapphire (without titanium).
The blue sapphires are due to the presence of pairs of charge transfer (with light excitation) between cations Fe2 + - Ti4 + or Fe 2 + - Fe 3 +.
Finally green sapphires are obtained by mixing blue and yellow.

Roger.

[John S. White]

I would add that the matrix for the blue corundum cannot be quartz because corundum and quartz cannot co-exist.

[MSrockhound]

Yes I agree about the quarts but the ruby specimen I hadn't had a chance to test yet and the white crystals were too small to see their habit without magnification. The sapphire is most definitely on a felspar matrix as there are several well terminated crystals in it.

I believe alex chauss hit the nail on the head, it appears to be almost a perfect match for the Polar Ural locality according to mindat pictures of a similar piece.

[Peter]

Geeees

Khit Ostrov https://www.mindat.org/gallery.php?loc=4436&min=1136


Polar Ural has a locality Rai-Iz where very beautiful red ruby occur and they have a very strong deep color, different morphology and different matrix.

Believe whatever you like ;)

[ACC79]

This link with Rai-Iz ruby specimens: https://www.webmineral.ru/deposits/gallery.php?id=76&filter=2158&gallerymode=full
This link with Khit Ostrov ruby specimens https://webmineral.ru/deposits/item.php?id=7
(links normalized by FMF)
PS better late than never ;-)