CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: Fake gem rough
PostPosted: Fri Mar 13, 2015 6:47 am 
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Over the years I have accumulated a small collection of fake gem rough specimens for teaching. I will post photographs of them here, and invite others to contribute additional examples in the hopes that this might form a useful visual collection.
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Fake gem rough 02.2.jpg
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This is a sample of parcel of 'emeralds' ostensibly from Zambia, ranging from 10-15 mm in length. Most of them are coated with biotite mica and have striations along the length. Superficially they are pretty convincing.
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Fake gem rough 03.2.jpg
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With some of the 'stones' turned to face the viewer you can see several tell-tale features. Emerald crystals are hexagonal, not pentagonal, so when lying on a prism crystal face a face and not a ridge should be facing up. You can see indentations on the 'ends' of the 'crystals', and the majority of the specimens have them. Natural emerald crystals, unless the ends are broken, have flat faces, not rounded indentations.
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Fake gem rough 04.2.jpg
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A close-up view through the polished face of one specimen shows the swirls of numerous bubbles typical of glass. These fakes are made from glass poured into mica-lined molds, and the indented ends are due to contraction as the glass cooled. No RI determination is needed to identify these as fake, but for interest it is 1,520.
[continued]


Last edited by Duncan Miller on Fri Mar 13, 2015 8:17 am, edited 2 times in total.

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 7:00 am 
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Fake gem rough 05.2.jpg
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Here is another photograph showing the pentagonal outlines of the 'stones' and the indented ends due to cooling of the glass in the mold. Some of the examples in this batch are indeed hexagonal, so it is mystifying that not all of them are.
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Fake gem rough 06.2.jpg
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This is a photograph of a 25 mm long 'terminated tourmaline crystal' bought by a customer of mine at the Klein Spitzkopje in Namibia. Apart from having eight sides (tourmaline commonly has three or six) it has abraded faces and a couple of small round bubbles (mid lower left). Through crossed polarizers the 'crystal' clearly was optically isotropic.
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Fake gem rough 07.2.jpg
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How about some chunky 'aquamarine crystals', obligingly covered in dirt, bought by a geologist (!) in Mocambique. The largest is 60 mm long.
[continued]


Last edited by Duncan Miller on Fri Mar 13, 2015 8:18 am, edited 2 times in total.

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 7:33 am 
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Fake gem rough 08.2.jpg
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Here is another view of the 'aquamarine', showing that they are not hexagonal, but rather irregularly pentagonal in cross section. Beryl crystals typically are hexagonal in cross section.
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Fake gem rough 09.2.jpg
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A closer view of the end of one specimen shows strongly choncoidal fracture, suggesting glass.
Attachment:
Fake gem rough 10.2.jpg
Fake gem rough 10.2.jpg [ 138.39 KiB | Viewed 2765 times ]
An even closer view shows round bubbles below the surface. These are chunks of greenish glass, with roughly ground and battered faces, lightly coated in reddish soil. They display no dichroism and between crossed polarizers they are optically isotropic.
[continued]


Last edited by Duncan Miller on Fri Mar 13, 2015 8:44 am, edited 1 time in total.

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 7:56 am 
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Thank you, Dunkan!

Polariscope reaction is isotropic or amorphous?

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 8:08 am 
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GSK wrote:
Thank you, Dunkan!

Polariscope reaction is isotropic or amorphous?

Transparent amorphous materials are optically isotropic. Thanks, I have made appropriate edits.


Last edited by Duncan Miller on Fri Mar 13, 2015 8:46 am, edited 2 times in total.

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 8:16 am 
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This is my last example.
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Fake gem rough 12.2.jpg
Fake gem rough 12.2.jpg [ 119.07 KiB | Viewed 2756 times ]
This 35 mm diameter nodule was part of a parcel that did the rounds of jewellers in Cape Town, offered to them variously as ruby or garnet. I begged this example off a friend of mine for bursting his eager bubble. Anyone who has handled ruby or garnet gem rough would be highly suspicious of the size, the roughly abraded edges of this supposedly hard material, and the obscuring pebbly matrix.
Attachment:
Fake gem rough 13.2.jpg
Fake gem rough 13.2.jpg [ 142.69 KiB | Viewed 2756 times ]
A closer view shows the large, conchoidal fracture surface, the heavily abraded exposed edges, and some round bubbles (top right). This too is glass, coated with an artificial 'matrix' of sand grains and pebbles in resin.


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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 8:47 am 
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Thanks for this; it's quite instructive. To me, the first aquamarine is the most convincing; the "terminated tourmaline" the least. Had I been offered the aqua, say by an internet seller, and with only the photo to go on, I'm not convinced I would have given it the necessary second look. Your post is a welcome reminder to always be on critical guard. Do keep them coming!

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Hans Durstling
Moncton, Canada

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 12:31 pm 
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A nice, sobering list of examples. Thanks for posting these.

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 Post subject: Re: Fake gem rough
PostPosted: Fri Mar 13, 2015 3:53 pm 
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The thing that I like the most is tat you point out why it is fake. ESPECIALLY something that can be done wit few instruments. (like crystal form).

Now I just need a way to learn it all.... or get started on cheat sheets..... Part of my problem is that I no longer trust my memory. It is worse when I am so sure I do not question it. I recently had hexagon and octagon backwards.....

I think that I need the cheat sheet that has:
Topaz Orthorhombic but I then need a picture of what that is.....


If you can avoid it do not get brain tumors..... :D


Please keep this thread alive with more fakes, and how you know.


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 Post subject: Re: Fake gem rough
PostPosted: Sat Mar 14, 2015 12:30 am 
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Brilliant! Thanks for this thread!


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 Post subject: Re: Fake gem rough
PostPosted: Sat Mar 14, 2015 3:07 am 
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wilsonintexas wrote:
The thing that I like the most is tat you point out why it is fake. ESPECIALLY something that can be done wit few instruments. (like crystal form).
As with any gem (or fake) identification, the more diagnostic characteristics you can determine the better. But all four examples above are glass, and to recognise glass all you need is a loupe, a light source, and a trained eye to recognise the typical swirl marks (due to slight variations in composition) and round gas bubbles. This combination is pretty much diagnostic for glass. If you are handling rough, then a scratch test can help. Wonky crystallography should arouse suspicion, but lots of natural crystals do not display ideal shapes. Surface characteristics like abrasion and lustre also can help, as can a crossed pair of polarizers. Of course, there is plenty of fake natural gem rough that is not glass - 'diamond' crystals cleverly carved out of cubic zirconia, tumbled synthetic sapphire added to alluvial concentrates, purple fluorite in parcels of amethyst, synthetic periclase (MgO) masquerading as peridot, etc. Perhaps others can add further examples.


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 Post subject: Re: Fake gem rough
PostPosted: Tue Mar 24, 2015 10:02 am 
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Nice topic

Quote:
flux grown and hydrothermal grown synthetics do show crystalline facets, but synthetic crystals grown by melt processes (Verneuil, Czochralski...) occur as single rounded cylindrical masses called 'boules' which do not look anything like a natural crystal.
However, let's note that such 'boule' can be cut into the shape of a natural looking crystal (with engraved striations to imitate natural growth markings), which is then glued into a natural or reconstituted matrix, or rounded to look like alluvial. Sometimes, to make the stone appear more natural, it is quench cracked so to produce natural-looking fractures in the stone (which fractures may also be filled with some ochre-colour dye or resin so the stone looks like naturally included).


Here are some flame fusion corundum shaped to imitate rough:

http://i223.photobucket.com/albums/dd21 ... C_6522.jpg
synthetic ruby grown by flame fusion process, which has been cut into the shape of natural-looking crystal and glued in a reconstituted matrix (made of rock powder mixed with resin).

http://pj.b5z.net/i/u/2102552/i/synthetic_rough.1.jpg
another synthetic flame fusion ruby, which was cut in the shape of a natural crystal, engraved with striations (note the dings and the dirt to make the stone look more genuine).

http://www.gia.edu/cs/Satellite?blobcol ... inary=true
synthetic ruby grown by flame fusion process, which has been cut into the shape of natural crystal and glued in marble matrix.

http://www.gia.edu/cs/Satellite?blobcol ... inary=true
synthetic ruby versus natural ruby composite stone (triplet), shaped to imitate rough: a slab of flame fusion synthetic ruby was sandwiched between to thin slices of natural ruby showing hexagonal growth figures, the whole assembly was then cut and rounded a bit to look like a rough piece, and the sides of the stone were engraved with striations.

Another case worth mentioning is synthetic overgrowth over natural crystals. Here's a natural quartz which damaged terminations were re-grown via hydrothermal process (natural quartz overgrown by synthetic hydrothermal quartz):
http://www.mineral-forum.com/message-bo ... 96_993.jpg


PS: besides synthetics and imitations, another thing to keep in mind when buying rough is that rough stones can be treated (i.e. irradiated, heated, filled, dyed, coated, diffused...)


Last edited by cascaillou on Wed Dec 09, 2015 4:22 pm, edited 2 times in total.

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 Post subject: Re: Fake gem rough
PostPosted: Tue Mar 24, 2015 10:37 am 
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an interesting antique gallo-roman glass slag (note devitrification figures) that was dug out of the ground:

Image

another antique glass slag:
Image

the funny thing is that these are not intentional fakes, but people might think they are natural since they came out of the ground.


Last edited by cascaillou on Thu Mar 17, 2016 9:51 am, edited 1 time in total.

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 Post subject: Re: Fake gem rough
PostPosted: Tue Mar 24, 2015 11:43 am 
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Here is a photograph of the synthetic periclase I mentioned above, that was offered as peridot or epidote (!), "dug out of the ground right in front" of the vendor from Mocambique. The top face is a saw cut, but the front face and the side faces are cleavage faces, at 90 degrees to each other. It has cubic cleavage, so clearly is not peridot (or epidote). There are swarms of minute round bubbles, which you can't see in the photograph, and it is optically isotropic but the cleavage ruled out glass. This was a tricky one to identify positively and I had to measure both the RI (1.73) and SG (3.55) to nail it. (about 25 mm long)


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 Post subject: Re: Fake gem rough
PostPosted: Tue Mar 24, 2015 1:45 pm 
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One would think that such an unusual synthetic would be worth almost as much as peridot of that (non-optimal) color? Unless it's really big I guess.

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