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 Post subject: Synthetic Nanocrystal "emerald"
PostPosted: Fri May 13, 2011 8:15 am 
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I have been examining an oval 7.5 carat beautiful emerald green gem I bought off ebay for $10, sold as nanocrystal emerald .. there are lots of them. I wondered whether anybody else has studied them? or have been reported here (can't find any mention of them.

My preliminary findings are: RI 1.615 (very sharp shadow edge)
seems isotropic. But with polariscope seems to have double refraction (?). No dichroism. Color bluish green. Appears dark to black thru Chelsea filter. Spectroscope shows transmission only of green light. Very transparent and has some linear structure and a few tiny gas bubbles.

It is a new synthetic material described on the website of
http://rss-synstones.com
Nanocrystals are described as a composite glass-ceramic with general properties of:
RI 1.5 to 1.7, Density 2.7 to 3.2 g/cc Hardness 61/2 to 7
It says they make the material by HT synthesis 1500 to 1700 C of a mixture of oxides(inc silica, zirconia, alumuina, zinc,lithium &magnesium) widely diverse compositions, and the process produces xtallization of nanocrystals in an amorphous matrix. Color centers are located in the nanocrystals (presumeably less than 100 nm size). The nanocrystals identified by X-ray diffraction are Mg spinel , gahnite (zn-spinel), sapphirine (monoclinic Mg,Al,silicate).
It doesn't say what the proportion of nanocrystals to glass matrix is.
In nature, gahnite is colored dk green to leak green to blue
Sapphirine is pale to dark green to blue.

This poses a problem in gem testing which is dependent on optical properties of light violet 400 to red 700 nm, since the nanocrystals are smaller than its wavelength and are uneffected by it, but they do diffract X-rays.

The green color of macro-syn spinel is supposed to be due to a combination of Mn and Co (Cr gives red as in ruby).
A pink variety is also available.

Any more information on these nanocrystals would be welcome.
Allano


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Fri May 13, 2011 9:15 am 
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hi and welcome to the forum :D

allanotaylor wrote:
My preliminary findings are: RI 1.615 (very sharp shadow edge)
seems isotropic. But with polariscope seems to have double refraction (?). No dichroism. Color bluish green. Appears dark to black thru Chelsea filter. Spectroscope shows transmission only of green light. Very transparent and has some linear structure and a few tiny gas bubbles.


your findings seems consistent with glass, IMO, (double refraction could be ADR)

Quote:
This poses a problem in gem testing which is dependent on optical properties of light violet 400 to red 700 nm, since the nanocrystals are smaller than its wavelength and are uneffected by it, but they do diffract X-rays.


it's my understanding "gem testing" is never dependant on optical properties only, can you elaborate, please?

Quote:
Any more information on these nanocrystals would be welcome.


yes, definitely, i'm curious too.

ciao
alberto

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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Fri May 13, 2011 10:04 am 
I'm curious about the name 'nanocrystal'. To me this means crystals in a size range below one micrometer (1*10-6 of a meter). Crystals down to a size of < 10nm can indeed be made and manipulated - but this is not what the reseller is claiming. Further, Zirconium Oxide will not melt at anywhere near the temperature range quoted.

Frankly, without a much better description of what the stuff is and how it is made, I'd not take the description at face value. Some resellers of gemstone imitants are notorious for publishing pseudo-scientific claims in the marketing of their stuff.

I note that the stuff is made in the Czech Republic, an area that has a long tradition of glass-making and, indeed, produces some very pretty coloured glasses.

Welcome! :D


Last edited by Kerensky on Sat May 21, 2011 9:48 am, edited 1 time in total.

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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Fri May 13, 2011 10:13 am 
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I also suspect this material is glass If you control the cooling process and slow it down then some of the melt will indeed begin to crystalise, If these crystals don't grow very large then I guess the term nanocrystalline could be used

It all sounds like a marketing scam to me


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Fri May 13, 2011 1:06 pm 
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I want to share some information and pictures of man made material which is my friend call nanocrystal

The material is sold in the name of Emerald in India and Pakistan and locally name is (Pana) which means Emerald. The RI of the material is 1.54. Mostly this material comes from china and Jewelers embedded the material in rings or jewellery and sold in the name of Natural Emerald. The Faceted stones edges are slightly curve which means that the material is polish on buff or leather lap.

With best regards

HUK


Attachments:
nano crystal (2).JPG
nano crystal (2).JPG [ 39.47 KiB | Viewed 14480 times ]
nano crystal (3).JPG
nano crystal (3).JPG [ 42.62 KiB | Viewed 14480 times ]
nano crystal.JPG
nano crystal.JPG [ 42.38 KiB | Viewed 14480 times ]

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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Fri May 13, 2011 6:17 pm 
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Hi Osman
Thanks for the nice fotos of "Pana" emerald that you say is common in Pakistan and India , having an RI of 1.54, and rather poorly faceted.
I don't think this is the same material that I describe and have bought as "Nano crystal emerald" from eBay.
I have a similar 30 carat oval emerald green paste (very nice) that has an RI of 1.52, isotropic, but is not the same as the "nanocrystal" emerald as is now on market with RI of 1.62.
Re comment on very high mp of zirconia .. all the oxides mentioned in the mix have high melting points, but the mixture of them could well give a homogeneous melt at 1500 to 1700 degrees C. It seems an incipient crystallization is allowed then the melt quenched to give the glass-ceramic product.
Maybe in Nature the material could be compared to chalcedony which is cryptocrystalline quartz with some amorphous matrix.? Cheers Allano


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Sat May 14, 2011 5:17 am 
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Quote:
It seems an incipient crystallization is allowed then the melt quenched to give the glass-ceramic product.
Maybe in Nature the material could be compared to chalcedony which is cryptocrystalline quartz with some amorphous matrix.? Cheers Allano


Allano,

you already checked whether it is an aggregate of small crystals (polycrystalline) or an amorphous substance (just plain old glass).

From the Gemology Project:

Quote:
Operation of the polariscope and possible observations
With the polarizer and analyzer in crossed position, turn on the light source and place the gemstone on the rotating platform just above the polarizer (this platform might not always be present, in which case you use your tweezers).
Observing the gemstone through the analyzer while slowly turning the stone will give you 4 possibilities.
1. The stone appears dark throughout a 360° rotation.
The stone is isotropic (single refractive).
2. Throughout a 360° rotation the stone blinks 4 times, light and dark.
The stone is anisotropic (double refractive).
3. The stone will appear light all the time.
The stone is a microcrystalline or cryptocrystalline aggregate (like, for instance, chalcedony).

4. The stone will show anomalous double refraction (ADR).
It is isotropic (single refractive).


The first 3 behaviors should pose no problems for the inexperienced user, but the latter (ADR) can be misinterpreted and cause one to think the stone is double refractive.


You are observing ADR, so, with the info above, you should be able to answer your own question.


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Sat May 14, 2011 6:14 am 
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Further thoughts etc on "nanoemerald"
I have no reason to doubt the technical information provided by the manufacturers (http://rss-synstones.com) which is quite detailed eg . New synthetic material developed by hi-tech nanocrystal technology.
"Nano-emerald" is a composite glass-ceramic material.
See Wikipedia (glass-ceramics) which have a multitude of uses, starting off with Corningware cookware, now ceramic stove tops, telescope mirrors and rocket nose cones ... so why not emeralds?
A homogeneous glass melt is made and then carefully heat treated to develop a crystalline phase to an extent to get desired properties, like near zero coefficent of expansion, high strength etc You may have 70 % glass and 30% crystalline phase, or whatever. Glass ceramics (typically porcelain, bone china has mullite in glass) can be made opaque, translucent, transparent and colored.
This seems to explain why nanoemerald is isotropic with RI 1.615 on refractometer and shows no dichrosim, yet is doubly refractive when viewed between x-polarizers?. I have with the polariscope compared 4 gemstones together viz green paste, green synthetic spinel, blue synthetic corundum & nanoemerald. The spinel and paste remain dark on rotation, but the corundum and nanoemerald show clearly 4 times dark and 4 times light on rotation, hence it contains some doubly refractive component?
The manfacturers say the crystalline component contains Mg-spinel, Gahnite (zn-spinel) & sapphirine (a MgAlsilicate... nothing to do with sapphire .. check Dana) and give x-ray powder diffraction patterns to verify it.
Surely the GIA have reported on nanoemerald by now ??? You need to crush one to a powder and x-ray it to determine the crystalline component and get a rough estimate of the ratio of glass to xtals (25%, or 50% xtals etc).
The spinels are isotropic so we must look to sapphirine (monoclinic) for the double refraction effect, but I dont know how this is effected by being polycrystalline and very small xtal size.
Additional info obtained from today's playing around with it.
Fluorescence: None with blue LED or long wave UV laser.
Thermal probe: low thermal conductivity, giving the same response as green glass, green syn spinel, syn corundum.
Spectroscope: nothing distinctive, maximum green transmission.
Note on color: a magnificent bluish green, much more attractive than green synthetic spinel and green paste.
Chelsea filter: remains dark/black with perhaps a faint red tint rather than green.
Dark field illumination shows up the inclusions very well.
Many very fine black lines (very fine particles?), end on of view of patchy very thin curtains in parallel arrangement and very slightly curved, with scattered tiny gas bubbles. Some strings of bubbles. An interesting "jardin"!
So, why make "nanocrystal emerald?" (I'm not on the payroll)
I think the color is exceptionally good.
The material can be mass produced very cheaply.
Hardness given is 6 1/2 to 7 which is better than green paste (5 1/2)
Lets see what eventuates, in green and other colors.
Cheers
Allano


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Sat May 14, 2011 11:25 am 
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Gems & Gemology reviewed this material in their Summer 2010 issue, pages 156-157.
To summarize:
"Nanogems"-A New Lab Grown Gem Material
This material was originally developed in the 1970s where it was used as a surface for cooking ranges. It is a glass-ceramic material having properties which make it useful for industry, such as negative thermal expansion.
It consists of nanometer sized particles of oxides and silicates, grown within a glass matrix.
Using this concept, a Russian manufacturer, Formica LLC, with a factory in Bangkok has produced this material for use in jewelry. They call it Nanogems.
At the Tucson Gem Show 2010, Formica LLC donated four samples to the GIA for testing. Two blues and two greens, both faceted and vividly colored, with a Mohs hardness of 7-7 1/2.

Standard Gemological Test Results are as follows:
RI (blue) 1.621
RI (green) 1.629
SG: 3.02-3.07
Polariscope: Aggregate Reaction
Fluorescence: Inert LW and SW, no phosphorescence
Spectroscope: blue: absorption bands:545, 583, 624
green: absorption bands:593, 633
Microscopic Observation: Pinpoint inclusions and conchoidal fracturing. When illuminated with fiber-optic light, all had a rather milky appearance, cause by the scattering of light from the nanocrystals.

LA-ICP-MS determined the chromophore of the blue material to be cobalt, and the green, nickel.

The issue for the gemologist, is being able to separate this material from glass which is typically used as gem simulants. :smt102

The GIA observed that in the stones they tested, aggregate polariscope reaction coupled with strong graining was diagnostic in separation, but noted that all examples of this material may not possess these characteristics.
In that case, positive separation would depend on results from X-ray diffraction. Which, for most of us not having this technique in our labs, would be a costly, and eccentric determination.


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Sat May 14, 2011 6:20 pm 
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Thanks Barbra for finding the GIA report (2010) on "nanoemerald" which is comforting and reassuring.
I think that the faceted stones now available on eBay are a new and improved version of the same material.
For example, my 7.5 carat specimen has no milky appearance nor has strong graining,... it is perfectly transparent.
I could not detect any absorption bands with the spectroscope.
Re the green chromophore... GIA says it is nickel, but nickel usually gives an apple-green color (in solution, dyed agate and in synthetic beryl). My nanoemerald is a magnificent bluish green so I suspect a different chromophore.
Also, what does the analytical method LA-ICP-MS stand for?
Many thanks for your assistance in helping to identify this new gem material.
Regards, Allano


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Sun May 15, 2011 11:06 am 
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allanotaylor wrote:
Thanks Barbra for finding the GIA report (2010) on "nanoemerald" which is comforting and reassuring.

You're welcome
Quote:
Also, what does the analytical method LA-ICP-MS stand for?

Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Quote:
Many thanks for your assistance in helping to identify this new gem material.
Regards, Allano

Well, I would not necessarily term this a "gem material".
It is an inexpensive, glassy artificial product.
It can be made abundantly.
I wouldn't call it a "gem", just as I would not refer to rhinestones as "gems".
:)


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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Mon May 23, 2011 7:51 pm 
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[-X " a gem can be thought of as any material which is used for adornment or decoration, especially when cut or polished" <----quote from gem-a gemmology 101! :twisted: :smt110

ok gonna hide now! barbra is gonna get out teachers twitchy stick 8-[

:wink:

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 Post subject: Re: Synthetic Nanocrystal "emerald"
PostPosted: Mon May 23, 2011 8:36 pm 
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Quote:
a gem can be thought of as any material which is used for adornment or decoration, especially when cut or polished" <----quote from gem-a gemmology 101! :twisted: :smt110

I think they sort that out by the time they get to the Diploma Course. :wink:


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