Thursday, December 13, 2007

Nailhead spicule in yet another Natural emerald

by Chaman Golecha

"A STUDY OF NAIL-HEAD SPICULE INCLUSIONS IN NATURAL GEMSTONES" was our first mark in the index as a main article (earlier reports were in the short GNI section) of the Gems and Gemology (A quarterly of the Gemological Institute of America, USA). The article published is published in the current issue of the magazine (Vol.43, No.3, Fall 2007). One may read the abstract here.

Within few days of receiving the magazine, we encountered another Natural emerald with prominent true Nail Head spicules. Since, the article was already published and reporting this would be of no use, I decided to kick start my blog with this. What follows is a report on that emerald.

Figure: Nail Head spicule in Synthetic emerald, courtesy of GIA website.


We encountered this stone just 3 days back (10th Dec 07). The specimen weighing 3.71 cts, oval mixed cut was submitted for testing at the Gem Testing Laboratory, Jaipur, India. Initial analysis using standard gemmological techniques revealed properties (Refractive Index, Specific Gravity, Spectrum, Polariscope, Dichroscope reactions etc.) typical of emerald, Natural or Synthetic. Magnification is the most important feature in the separation of Natural and synthetic gemstones. This specimen was no exception.

Upon magnification, several parallel zones were observed with some elongated inclusions oriented perpendicular to the zones. Examination of these elongated feaures revealed NHS inclusions. This emerald had much clearer and well developed spicules than the one we had reported in the G&G.

Figure: Parallel zones and Nail head spicule inclusions.
.

Some of the spicules had a very long cone along with clear phase. The base of the inclusions was made of cluster of crystal inclusions which somewhat appeared like flakes of some brown mineral. Due to lack of Raman, we could not determine the nature of the inclusions. All the inclusions were oriented along the optic axes which was determined by observation along crossed polars.

Though almost all the spicules had their cones pointing towards the same direction, a few of them were oriented at 180 degrees i.e. exactly opposite direction (still along the optic axes).

View along girdle revealed undulating features "chevron" effect as in the figure. Both the Nail head spicules and "chevron" growth features have traditionally been associated with hydrothermal synthetic stones. However this specimen proved to be an exception. The natural identity of this stone was made by the presence of zoning features, liquid films, crystal inclusions (mica?) etc. Further confirmation was obtained by FTIR which revealed features of Natural emerald.

Figure: Undulating pattern somewhat resembling chevron growth patterns.

Time and again, I have encountered features which have traditionally associated with Natural in Synthetic and vice-versa. Such specimens, time and again reminds one of careful and complete examination. Also one should never rely on a single feature to make an identification and such a stone could easily mislead a novice gemmologist.

P.S.: Click on the images to magnify them for a clearer view. Comments are welcome...!!

Acknowledgment: Mr. Gagan Choudhary and Mr. Mustaqueem Khan for all the co-operations and helpful discussions.


PHOTOMICROGRAPHS OF OTHER INCLUSIONS IN THE ABOVE SPECIMEN

More Nail head spicule inclusions:



Sheen observed along parallel zones:


8 comments:

Unknown said...

Mr. Golecha, i would like to thank you for sharing with us, such an important information.

you (along with GAGAN SIR, MUSTAQEEM SIR N MEENU MA'AM) have always been guiding us through the latest discoveries related to this field. which is very helpful in doing are day to day business.

Thanks a lot.
Arpit
Ex-GTLian

meenakshi chauhan said...

Hello Mr.Chaman Golecha.
As you wrote that those emeralds were having liquid films etc, have you observed some difference in those liquid films also, as once i have seen one fingerprint in one synthetic emerald which was showing hound's tooth like pattern. can we identify such emeralds as natural or synthetic without FTIR.

Cant we have such liquid films in synthetic emeralds.

and secondly i want to ask that can manufacturers put mica or anyother solid inclusions Intentionally.
Hoping for prompt reply
Thank you
Meenakshi Chauhan, MDGI

Golecha said...

@ arpit...thnx...gud to know tat u follow these updates closely....!!

@ meenakshi...Wel the liquid films that were observed in the specimen were "typical" of natural. There were oriented along the basal planes and very similar to those encountered in earlier cases.

Regarding hound's tooth features in natural emeralds, wel even we have encoutered such a specimen and reported in G&G around 2 years earlier. (if you want shal inform bout the issue soon).

Regarding identification without advanced instruments, it may sometimes prove to be tricky, but it all has to do with CAREFUL AND COMPLETE EXAMINATION.

Lastly, as of now, I am not aware of mica being intentionally added by manufacturers...would love to learn about it if you have heard of any such report. (I can analyze it for you in case you have a sample). Hope tat helps
Golecha

Richard W. Wise said...

Golecha,
Congratulations, you certainly kicked off you first blog with a bang. Keep up the good work.

Richard W. Wise

Richard W. Wise said...

Golecha,
Congratulations, a great kick off. Keep up the good work.

Richard W. Wise

Golecha said...

@ R.W.Wise (the king of gemological blog)
Thnx a lot for the encouraging comments...am thrilled... !!!

BTW, I took a lot from your blog while preparing the presentation on Paraiba tourmalines (the one for which i gave the link on gemologyonline.com)and as everybody else find your write ups very impressive...it also has to do with the inspiration i recieved to start off my blog....thnx again..

Anonymous said...

I have just finished writing 'The Handbook of Gemmology' which will feature the award winning photographs of renowned Gem Photographer Tino Hammid. I am hopeful that the book will be used by various Gemmological Associations worldwide as a textbook.

I would love to use two photographs included in your blog. The first is the nail-like inclusions found in Linde Synthetic Emeralds and the other is the 'Chevron' effect'. They are photos 3 & 4 in the blog.

I was wondering if these photographs are yours and if so, would you grant me permission to use them. If so, do you have high resolution images that I could use?

In return we will not only include you in the 'Photographs Acknowledgements' section but also include a link on the book website to any URL you wish that is connected to you.

I look forward to hearing from you at your earliest convenience at geoffdominy@yahoo.ca

Yours sincerely,

Geoffrey M Dominy FGA (with Dist)

Golecha said...

Dear Mr. Geoffrey M Dominy,

I have sent you a mail.

Golecha