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Lukeness

Gemstone 101

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alloway65

Good day,

Re blue/green & Indicolite Tourmalines, why do a lot of these gemstones have proportions outwith the "normal" gemstone standards. They have a length to width ratio of between 3:1 & 4:1.

The reasons for this wouuld be much appreciated.

:roll:

Thanks

David

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Lukeness

Because it maximises cut based on the tourmaline crystal shape.

And the stone does pull it of pretty well...

lol

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alloway65

Thanks Luke, I thought it might be something like that. :D

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lisaa

Hi Luke,

 

Could you post how an amateur collector can join the Gemological Society or its counter part? Or pm me if you don't want to post, please.

There is so much to learn. :?

 

Thx

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Lukeness

Hi Lisaa,

 

Anyone interested in joining can PM me for details.

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travellingstudent

I've travelled Myanmar. Wicked place!! and lovely people. :lol:

I recon the embargo is only in place since the Burmese refused to sell at rock bottom prices to the US. Unlike during our sanctions.

Contrary to what the international community would like people to beleive, not everyone in Myanmar is poor and miserable. There'll be alot worse off if they open up and get exploited like the Cambodians.

 

Anyways....they have beautiful stones but the majority of the good stuff stays in the country. Wealth is held in gems all over SE Asia.

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Lukeness

The real problem there is who is getting the money. The border to Thailand is also very porous so a lot still gets through. As with the drug trade there.

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Lukeness

Temperatures Necessary for Heat Treatment:

 

Temperatures Necessary for Heat Treatment:

Aquamarine: 450 degrees Celcius changes the valence state of the iron as described below

Amethyst to Citrine:: 450 degrees Celcius

Reddish Brown Zircon to Blue: 1000 degrees C in a reducing (oxygen free) environment

Reddish Brown Zircon to Colorless 900 degrees C in air

Orange Beryl to Morganite: 400 degrees C

Yellow and Brownish yellow topaz to Pink: 550 degrees C

Topaz (all colors) to Colorless:1000 degrees C

Dark Green Namibian Tourmaline will brighten Significantly:370 degrees C

Brownish Green Zoisite to Tanzanite:370 degrees C

Sapphire containing titanium to develop or brighten color:1600 degrees C

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flammaefata

Help on gemstone identification

 

I have five stones that my mother bought about ten years back and she has always proclaimed that they must be sapphires, rubies, emeralds and such. To finally settle this I sent the gems to eppie5064 so that he could take refractive index and specific gravity measurements to identify the stones.

 

He got the following measurements and identified one as a tourmaline and another as a ruby, but we wonder what the other three might be. If you could please have a look at his results and see if you can identify the other three stones (even if they're just glass) I will really appreciate it!

 

I'm not entirely certain in which order he numbered the stones but I believe it is B A E C and then the second picture is of D.

 

The measurements (as quoted from eppie5064):

 

A 0.78 ct Blue Octagon

RI=1.63

Birefringence of about -0.018 (Doubly refractive)

SG =2.98

 

The data for stone A is consistent with tourmaline RI=1.614-1.666, Birefringence of -0.014 to -0.032 (Doubly refractive) and SG =2.82-3.32.

 

B 0.755 ct Green Octagon

RI=1.645

Singly refractive

SG=2.89

Conchoidal (shell like) Fracture on 1 Corner and Swirl of Bubbles

 

C 0.44 ct Green Baquette

RI=1.655

Singly refractive (Anomalous)

SG=3.01

 

D 0.545 ct Green Marquise

RI=1.715

Singly refractive

SG=3.61

Facet joins worn, polish marks, Keel crooked

 

Stones B, C and D are all singly refractive. The majority of the crystalline singly refractive stones are made up by Spinel, Garnet and Diamond. I cannot find any crystalline singly refractive stones matching the data from stones B & C. That leaves Glass. Glass is singly refractive and has a very wide RI=1.44-1.90 and SG=2.0-4.5.

 

The bubbles and conchoidal fracture on stone B can be indicative of Glass.

 

Stone D’s data matches that of Spinel RI=1.712-1.762, Singly refractive and SG =3.54-3.63. There is a possibility that it may be glass as well. The worn joins and polish marks point to a stone much softer than spinel (spinel is 8 and glass is 5) and high value stones generally have high quality cutting and polishing. And the higher the RI of glass the softer the glass and the easier it wears down.

 

E 0.78 ct Red Baguette

RI=1.765

Doubly refractive

SG=4.02

Internally flawless under 10x loupe.

 

 

The data for stone E is consistent with ruby RI=1.762-1.778, Doubly refractive and SG =3.97-4.05. Because of its internal clarity under the loupe, it is either a very high quality natural ruby or a synthetic/man made ruby.

As always any help is higly appreciated!

58f5a71862434_flammaefata4stones.jpg.7ff5835e7fc5e7d026e949e9fce924cf.jpg

58f5a7186a97c_flammaefata1stone.jpeg.1f0a5c7e3da94ebe7dccde6bef014774.jpeg

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Lukeness

Hi,

 

I'll go through all the figures a in the morning and give you a more detailed answer. A little tied up right now.

On stone E. It needs to be examined under a microscope at at least 40x magnification to be able to tell if it is natural or synthetic. Various types of synthetics have been around a lot longer than most people realise, so it is still a strong possibility.

 

The spectra for stone D should be diagnostic.

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Lukeness

A 0.78 ct Blue Octagon

RI=1.63

Birefringence of about -0.018 (Doubly refractive)

SG =2.98

 

The data for stone A is consistent with tourmaline RI=1.614-1.666, Birefringence of -0.014 to -0.032 (Doubly refractive) and SG =2.82-3.32.

 

We need the minimum and maximum RI figures - RI is very slightly low for Indicolite or Paraiba. Possibly Liddicoatite but Specific Gravity slightly low.

Need to check under immersion for assembled stones

Need to check optic character under conoscope. Is it Uniaxial or Biaxial. Positive or negative.

 

 

 

B 0.755 ct Green Octagon

RI=1.645

Singly refractive

SG=2.89

Conchoidal (shell like) Fracture on 1 Corner and Swirl of Bubbles

 

Glass or assembled stone

C 0.44 ct Green Baquette

RI=1.655

Singly refractive (Anomalous)

SG=3.01

 

Glass or assembled stone

 

 

D 0.545 ct Green Marquise

RI=1.715

Singly refractive

SG=3.61

Facet joins worn, polish marks, Keel crooked

 

Glass or assembled stone, need a little more info to check possibility of Spinel. Magnification for inclusions and strain marks (glass) or anomalous double refraction on a polariscope would be quicker ways to distinguiguish.

 

Stones B, C and D are all singly refractive. The majority of the crystalline singly refractive stones are made up by Spinel, Garnet and Diamond. I cannot find any crystalline singly refractive stones matching the data from stones B & C. That leaves Glass. Glass is singly refractive and has a very wide RI=1.44-1.90 and SG=2.0-4.5.

 

The bubbles and conchoidal fracture on stone B can be indicative of Glass.

 

Stone D’s data matches that of Spinel RI=1.712-1.762, Singly refractive and SG =3.54-3.63. There is a possibility that it may be glass as well. The worn joins and polish marks point to a stone much softer than spinel (spinel is 8 and glass is 5) and high value stones generally have high quality cutting and polishing. And the higher the RI of glass the softer the glass and the easier it wears down.

 

E 0.78 ct Red Baguette

RI=1.765

Doubly refractive

SG=4.02

Internally flawless under 10x loupe.

 

Natural or synthtic corundum (Ruby/Sapphire)

All in all I'd say that the info you've received is probably correct.

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flammaefata

Thank you very much for your time and your reply.

 

Even though three of the stones are most likely only glass, at least they are still very pretty, and as I have inherited a bit of my mom's magpie personality I still like them a lot. And I'm very glad that I at last know what they are - I'm not one for believing every pretty stone is a rare and expensive beauty.

 

Once again thanks for sharing your knowledge!

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MsPlod

Treatments and "100% natural" gems

 

Two (or more) questions?

 

I am intrigued to know whether any treated gem may be advertised as "100% natural"?

 

There are many examples on BoB at the moment, where treated gems are advertised as natural and this is simply one example - so apologies to the seller - I am not singling him out - it appears to be a really beautiful stone treated with accepted treatments!

 

Rubies - RAVISHING!!! 3.36ct - 100% Natural Top Blood Red Ruby - R 10830.00 - MADAGASCAR for sale in Rustenburg

 

My understanding of the word "natural" implies that it is:

a) Not created by humans

b) Not treated in any way - other than cut and polished

 

I am naive...:P

 

The second question (in two parts) is whether a yellow (presumably citrine) and green (presumably prasiolite) bicolour gem is still called an ametrine or not?:confused: (The same for a purple and clear (no colour) "bicolour".)

 

The second part of the question is whether the ametrines with a VERY distinct line of colour distinction are ALL likely to be created gems or not?:confused:

 

Loads of questions? Any answers?

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Lukeness

Hi.

 

Natural gems are gems that are not man-made. To say 100% natural, in my mind, implies that they have also not been altered, by man. But there really is no hard and fast proper definition except that natural gems are gems that have been mined.

 

Ametrine is quartz with zones of Amethyst and Citrine. Other colours would be called bi-colour quartz.

One needs to be aware that most quartz available today is lab created. Also, fanciful colours (bright blue etc) are not natural at all. The more distinct the colour separation the better, within reason. If it is so sharp that it appears manufactured, well there's a good chance it was.

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MsPlod

Neat!

 

Succinctly answered, thank you Lukeness!!:)

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Lukeness

VS is usually used for very slightly included. They've just abbreviated the included too

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MsPlod

OK - thank you...

 

VS is usually used for very slightly included. They've just abbreviated the included too

 

Thanks Lukeness for the response!

 

If that is the case then what the seller is doing is to abbreviate incorrectly - since the actual gem description in the text of the the auction is SI - not VS.

 

Misrepresentation in the auction description I would say?:confused:

 

The seller seems to be doing this for a number of the auctions...

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Lukeness

This whole thing with different details in headings and actual listings really is terrible. It seems the are and are not appraisals, gems are VSI (sic) and SI etc. From some of the comments posted it seems that this has been used a few times as a loophole when things haven't gone the sellers way.

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MsPlod

Misleading descriptions...

 

This whole thing with different details in headings and actual listings really is terrible. It seems the are and are not appraisals, gems are VSI (sic) and SI etc. From some of the comments posted it seems that this has been used a few times as a loophole when things haven't gone the sellers way.

 

Yes, the seller definitely appears to be rather "free" with descriptions in general. There is also an interesting thing which I have noticed and commented on before which is that the seller used to advertise gems as follows - an example :

 

VS 1 .5ct

 

Meaning (in the actual auction description) that it was a VS1 gem weighing 0.5 carats - and these gems used to regularly sell for more than significantly larger gems of the same clarity (i.e. often R201 or so).

 

Ah well - it is always up to those of us who are learning about these things to check the heading AND description thoroughly!

 

Thanks again for your help Lukeness!:)

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MsPlod

Flawless

 

Thanks again for all the information Lukeness!

 

Wonder whether you would assist me with this one?

 

In my understanding the word "flawless" when applied to a gem would be described by a clarity rating of IF? The clarity rating of VVS implies that there are very very slight inclusions - is that correct?

 

I am a little confused by this auction advertisement...

 

Tanzanites - FLAWLESS VVS .34CTS OVAL TANZANITE for sale in White River (ID:22933697)

 

Since the description of the gem states that it has a clarity of VVS?

 

Could you assist me please? Many thanks:)

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Lukeness

In this case the term flawless might actually be 100% correct. In the GIA coloured stone clarity grading scale (which is what is being used) there is, strangely, no official F flawless (no inclusions [internal] or blemishes [external] under10x magnification) or IF Internally flawless (no inclusions [internal] under10x magnification) and the highest possible grade is VVS. Therefore it is conceivable that a VVS gem could be free from inclusions or blemishes at 10x magnification and while correctly being described ad flawless, it would only be graded as VVS. Let me know if I'm not making sense here, this is a little rambling... lol

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MsPlod

Did not know this thanks!!

 

In this case the term flawless might actually be 100% correct. In the GIA coloured stone clarity grading scale (which is what is being used) there is, strangely, no official F flawless (no inclusions [internal] or blemishes [external] under10x magnification) or IF Internally flawless (no inclusions [internal] under10x magnification) and the highest possible grade is VVS. Therefore it is conceivable that a VVS gem could be free from inclusions or blemishes at 10x magnification and while correctly being described ad flawless, it would only be graded as VVS. Let me know if I'm not making sense here, this is a little rambling... lol

Thank you very much, had no idea that the highest grade for GIA was VVS - learning in leaps and bounds - LOVE your rambles and you make plenty of sense thanks! :P

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