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 Post subject: Jeremejevite
PostPosted: Sun Dec 30, 2007 8:55 pm 
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How about a stone that "overlaps" with itself in a manner of speaking....

Someone showed me some beautiful crystals of jeremejevite from Namibia the other day - I hadn't seen any natural crystals before - these were maybe 2.5 cm long, a beautiful almost Ceylon blue with what looked like a beryl-like hexagonal prism habit. I read up a little on it and found some interesting detail:

Jeremejevite belongs to the orthorhomibic crystal system - though it shows a pseudo-hexagonal habit - which should make it biaxial. But faceted stones have shown a uniaxial negative optic character (texts variously list it as uniaxial negative and belonging to the hexagonal crystal system, with a note that it is anomalously biaxial with a very small 2v angle, also negative).

The differing optical properties are due to its growth zoning which is different for different localities: the optic character of the rim of the crystal is different than that of the core. From one locality the core is biaxial and the rim is uniaxial, but from another locality the core is uniaxial and the rim is biaxial.

So if you have the pleasure of studying a cut stone, one must keep in mind that the rim has been removed in the fashioning of it. It also goes to show that just one source book in your library is not enough.... and several sources might confuse one completely if you don't keep digging.

Just trivia for the New Year.


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PostPosted: Wed Mar 26, 2008 9:13 am 
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Hi all,



Casandra wrote:

Quote:
Jeremejevite belongs to the orthorhomibic crystal system - though it shows a pseudo-hexagonal habit - which should make it biaxial. But faceted stones have shown a uniaxial negative optic character (texts variously list it as uniaxial negative and belonging to the hexagonal crystal system, with a note that it is anomalously biaxial with a very small 2v angle, also negative).

The differing optical properties are due to its growth zoning which is different for different localities: the optic character of the rim of the crystal is different than that of the core. From one locality the core is biaxial and the rim is uniaxial, but from another locality the core is uniaxial and the rim is biaxial.


I took this picture of a jeremejevite interference figure.

Image


What do you think of this sort of 'double center uniaxial'. Is it a' small 2V' figure?

Thanks.


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PostPosted: Wed Mar 26, 2008 1:30 pm 
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Hi,

In uniaxial stones there is no "2V". This looks like a biaxial stone.
Could you tell us a bit about the conditions under which you took this image?

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PostPosted: Wed Mar 26, 2008 4:08 pm 
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Hi,

the conditions were 'normal' I guess:
crossed polars, strain-free glass conoscope

Casandra:
Quote:
the optic character of the rim of the crystal is different than that of the core

I remember now that in the Sinkankas 'Emerald and other beryls', the author mentions beryls (hexagonal hence uniaxial) with orthorhombic (hence biaxial) areas. I cannot give you more details as I don't have that book anymore. If anybody has that book, pages references would be welcome.

Now back to jeremejevite, here is another picture of an interference figure in the same stone as before (viewed from the opposite side as far as I remember).


Image

Have you seen this type of figures before?
Don't you think it can be related to an 'anomalous optic character'?


Thanks


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PostPosted: Wed Mar 26, 2008 4:39 pm 
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Hi,

There are such things as pseudo-biaxial and pseudo-uniaxial interference figures. http://users.skynet.be/jm-derochette/conoscopy.htm

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PostPosted: Thu Mar 27, 2008 5:54 am 
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Excellent link Doos,

Thanks


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PostPosted: Mon Mar 30, 2009 10:56 am 
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Dear all,
About jeremejevite, I would like to inform you that and article and a ongoing study are available currently on GIA Laboratory Bangkok website in the Lab research part of the website:

The On-going research article by J. Thanachakaphad:
http://www.giathai.net/lab.php

The Jeremejevite reference article by K. Scarratt &al (Gems & Gemology, 2001)
http://www.giathai.net/lab_research_publications_VP03.php

All the best,

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www.fieldgemology.org
www.conservationgemology.org

The views expressed here are V. Pardieu’s opinions and do not necessarily reflect those of GIA Laboratory Bangkok (http://www.giathai.net)where he is an employee since Dec 2008.


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PostPosted: Tue Apr 21, 2009 4:18 pm 
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A friend of mine, Elizabeth Price, brought over a ring she just had made with a 2.15 carat Portuguese-cut jeremejevite from Namibia. The stone is a very, very pale blue, very watery and has some hollow tube inclusions by one of the prongs,pictured below:
Image
Image

Some of the tubes seem to have a filler of some sort inside, and one tube (on the left) is bearded with euhedral crystals. Click the photo to enlarge.


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