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Identity HelpIs this "iolite" ( cordierite) ?
21st Apr 2012 18:47 UTCJohn R. Montgomery 🌟 Expert
Then I saw Jose Zendrera's question on p.15 of the Help Identify message board mentioning "iolite".
This specimen does not scratch with a knife.
It is 6cm x 3cm x 2cm
One end is flat and looks like it might have been sawed but I can see no marks ( to my UNtrained eye)
YOU CAN CLICK ON PHOTOS TO ENLARGE
thanks for any help
John
21st Apr 2012 18:54 UTCJohn R. Montgomery 🌟 Expert
ALSO can anyone tell me if this is a complete , partial or broken crystal or just a chunk?
thanks
john
21st Apr 2012 19:13 UTCDon Saathoff Expert
Nice chunk! I think cordierite is a good guess.
Don
21st Apr 2012 19:36 UTCJohn R. Montgomery 🌟 Expert
Hi Don,
MICROCLINE DOES NOT SCRATCH THE SPECIMEN BUT QUARTZ DOES.
The chap who gave it to me said it belonged to his father who was a gem cutter in Jaipur India.
Thanks
John
21st Apr 2012 19:46 UTCOwen Lewis
Here's a pic showing the typical pleochroic colours given by Iolie. This specimen was not even being viewed through a dichroscope but, unfiltered, through a microsope but the typical strong pleochomism shows up nicely in this shot.
21st Apr 2012 20:22 UTCWOLFGANG NOACK
regards
21st Apr 2012 21:01 UTCJohn R. Montgomery 🌟 Expert
Owen, I'm still googling to discover what some of those terms means... I'm a real novice). thanks for your input.
22nd Apr 2012 01:19 UTCJosé Zendrera 🌟 Manager
I think your stone is kyanite. Cordierite (iolite) is harder than quartz and is not documented in Nepal.
I bought some kyanite specimens in Kathmandu and they were sold as "kaynite", that sounds as your "ayolite" with Nepalese accent.
I hope this helps.
Greetings from another Nepal lover.
Kyanite from Kali Gandaki Gorge, Annapurna Region, Nepal. 7,1 x 1,8 x 0,7 cm.
This is the best specimen of the lot.
22nd Apr 2012 01:41 UTCJohn R. Montgomery 🌟 Expert
Nice to hear from you.
After checking scratch test (EDIT) I see that quartz definitely scratches this specimen. I also see in my books that Cordierite is listed as 7-71/2 hardness and quartz 7.
However microcline does NOT scratch this specimen. Would this be true of kyanite?
The gem dealer in Kathmandu who gave me this said it was from (not Nepal) but "the Hindu Kush". He also spelled it out as "Ayolite"...( not just verbal).
It may very well be kyanite but that was definitely not what he was saying. He said it came from his father.
By the way, I got some very nice kyanite in Nepal similar to your beauty ( see my home page).
thanks
John
22nd Apr 2012 06:59 UTCOlav Revheim Manager
Cordierite is well documented from Nepal, see amongst other Streule et.al (2008). "Melting and Exhumation of the upper structural levels of the Greater Himalaya Sequence and Makalu granite: constraints from thermobarometry, metamorphic modeling and U-Pb geochronology:" :
"The Makalu intrusion is multiphase and forms the structurally highest foliation parallel sheets of leucogranite along the top of the Greater Himalayan Sequence on the Nepal-Tibet border. It is comprised of massive Grt + Tur + Ms ± Bt leucogranites that also occasionally contain large cordierite crystals."
If you google "cordierite nepal granulite" you will find several papers discussing the cordierites in high grade metamorphic rocks as well as granites in Nepal.
To me, the rounded, glassy appearance of John's specimen point towards cordierite.
Olav
22nd Apr 2012 12:10 UTCJohn R. Montgomery 🌟 Expert
It does have a glassy appearance.
Here is some more pictures
22nd Apr 2012 15:55 UTCAndy Stucki (2)
I concur with Jose. It is without a doubt a kyanite. I've seen lots of this material, and this piece has the typical shape and color (and hardness, as you have observed). And pleochroism doesn't speak against kyanite as it is also pretty strongly pleochroic.
Andy
22nd Apr 2012 18:40 UTCJohn R. Montgomery 🌟 Expert
John
22nd Apr 2012 18:53 UTCStephanie Martin
The specimen appears to be the same mineral throughout so if you have a decent kitchen scale and basic equipment a specific gravity test should do the trick. There is a signficant difference between the two minerals.
Here is a link to a thread that discusses several ways of doing the same test, however Reiner's is probably the simplest.
Remember to not let the specimen touch the sides of the vessel.
http://www.mindat.org/forum.php?read,11,250282,page=1
Good luck!
Regards,
stephanie
22nd Apr 2012 23:00 UTCJohn R. Montgomery 🌟 Expert
thank you very much for this advice. I have performer the "Reiner" test as you suggested and came up with a specific gravity of 3.5294
The only trouble now is I don't know what this means!
If you see this could you kindly interpret this result or tell me how?
thanks
John
22nd Apr 2012 23:11 UTCBob Southern
Kyanite is anisotopic. In that it can have a hardness of 4.5 to 5 parallel to one axis,
and a hardness of 6.5 to 7 perpendicular to that axis.
Cordierite is isotropic so hardness of 7 in all directions.
Good Day
Bob
22nd Apr 2012 23:21 UTCStephanie Martin
Congratulations on performing a great result! Your data indicates your specimen is kyanite.
The density information can be found on the mineral data page. For cordierite the range would be between 2.6 to 2.66 and for kyanite
the range is 3.53 to 3.67.
As there is a significant difference between the 2 minerals, this would definitely point to kyanite. It would not be so defining if the minerals had similar densities, where absolute precision in the data may be more important.
I am glad this helped to resolve your query.
Regards,
stephanie :-)
22nd Apr 2012 23:26 UTCJosé Zendrera 🌟 Manager
John, your thread has a good ambiance! Nice to hear so many opinions!
Olav, thank you for cordierite information in Nepal, I just looked for it here in Mindat database. Could be that cordierite is present in small crystals and is documented by petrologist who study rocks under microscopy but rare in "big" specimens?
Two years ago I was in Kathmandu looking for gemstones and minerals information. I visited two geologist in the Departament of Mines and Geology of Nepal who gave me some publications where there is a list of gemstones and valuable minerals in all Nepal. I also asked to sellers when I bought some stones in most shops selling good specimens in Kathmandu. I found no mention to cordierite, not in text, not in oral information. Obviously, that don't mean it not exist, but I could not find them.
Anyway, my modest opinion about John specimen posted here is based on these characteristics:
- The "cut" at the end of the stone looks as a Kyanite termination (inclined, not flat as orthorombic cordierite).
- The small mica-like layers are also present in my Nepalese kyanite specimens.
- Oxide-like alterations are also present in my Nepalese kyanite specimens.
However, the color and opacity of John specimen are bit different from mine...
As Stephanie suggest, specific gravity test can clarify the matter.
Greetings.
Here two cordierites from Karakorum Mts, both bought to a Peshawar dealer:
4,1 x 2,0 x 0,8 cm. From somewere in Badakhshan, Afghanistan.
3,2 x 1,5 x 0,8 cm. From unknown locality in Pakistan.
22nd Apr 2012 23:29 UTCJohn R. Montgomery 🌟 Expert
Thank you so much for your assistance!!!
sincerely
John
....and hola Jose...it looks like you were correct! Congratulations!....
23rd Apr 2012 00:26 UTCJosé Zendrera 🌟 Manager
John, have to find another iolite...
Warm greetings.
23rd Apr 2012 13:02 UTCOwen Lewis
-------------------------------------------------------
>
> Cordierite is isotropic so hardness of 7 in all
> directions.
> Good Day
> Bob
Don't think so, Bob.
1. If Cordierite (coloured) was isotropic it could not be pleochroic - which it is, strongly. In fact, Cordierite is of the orthorhombic crystal system, which is anisotropic and biaxial. Yes, the hardness of Cordierite is (at the level of crudeness of measurement on Mohs's scale) omnidirectional.
2. Conversely, Diamond, which *is* isotropic can show a marked difference in hardness according to the direction of testing. The hardness of Diamond cannot be satisfactorily expressed (or assessed) on Mohs's scale but the hardness variation with test direction is about 30 GPa on a rational scale. That is a lot of variance. To put it in familiar terms, 30 GPa is approximately as much extra hardness as Corundum has over Talc!
The only minerals that are isotropic are either amorphous or of the cubic crystal system.
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