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 Post subject: Rough Emerald identification
PostPosted: Fri Nov 07, 2008 1:23 am 
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Hi there,

I would to know how can I identify an emerald in rough form say it comes embedded in a 45 kg rock!! is there a way to make sure with simple gemological tools... like chelsea filter, dicroscope 10x loup and fiber optic light to chk incl. Is there a way to ID without taking R.I.?

If you can give me some clue and or website which can help me kindly help.

Thanks alot
Sera

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 Post subject:
PostPosted: Thu Dec 11, 2008 4:02 pm 
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This question has been unanswered for quite a time now, even I seem to have overlooked it although I usually read everything related to emeralds.... So I´ll take a shoot and try to help.

As I understand it, there is a large piece of rock with an suspected emerald crystal on the table to be looked at.

1.) Origin

Is the origin of the rock itself known? If yes, check up the location list on http://www.mindat.org/min-1375.html. If you have a hit there already, the chances are growing that there might be a emerald specimen on the table.

2.) The host rock

Emeralds form in specific geological environments only. That´s why they are not found as plentiful as other gems like garnets or quartzes. Since you use the term "embedded" describing the position of the crystal in the rock, I assume the crystal has grown inside the surrounding host rock.
This would be a porphyroblastic growth, a term that applies to crystals that formed inside the melt during a metamorphosis of the host rock. Basically the crystals grow like seeds inside this melt by taking all elements needed for the emerald formation out of it. Such host rocks should be metamorphic type of rocks.

Emeralds in such formations nearly always are heavily included since they take in the surrounding crystals of the melt while growing, forming a vast variety of inclusions. Color of such emeralds would be from light milky greenish blue to very dark forest green, almost black, depending on the host rock. The crystal faces of our suspected emerald would be uneven, looking snakeskin - like under a loupe.

If there is a crack, or a little cavern in the rock and the crystal sits therein, along with other minerals we have the second type of emerald growth, the hydrothermal formation. The elements needed to form an emerald are brought into such a crack, rift or cavern by a liquid solution. Within the hole inside the massive rock the crystals can form to very big individuals, and, since there is less interference with the surrounding rock, are often very clear and beautifully colored. This is just for the record, If such a piece was an our virtual table, the question would have been formulated a bit different.

Also check the crystal environment with a loupe or a microscope, to be sure that it is not a glued in piece, things like that happen all the time.


3.) the Crystal itself

Emeralds are beryls that are colored green by traces of chromium.
Beryls have a very distinctive outer form, they occurr as hexagonal prisms. These six-sided crystals are easy to identify, even if only a few sides of the crystal are seen on the surface of the rock. You can use the button crystal systems on the left side to check if the outer form of the crystal we have is right.

The crystal should be, aside from having the right outer form, green. The green can be very faint, neon - like, more like grass or even sometimes hidden behind a Overtone such as blue or yellow.

But halt: Not every green beryl is a emerald: there are some crystals colored by vanadium instead of chromium that are not called emeralds, according to gemological practices.

And here we have the tool how to distinguish the two from each other: (And right now i´m leaving my territory and get on thin ice, please correct me if I´m wrong on this guys) look at your crystal through a chelsea filter. There should be a reddish glow seen on the crystal if some chrome is present. With vanadium, there is no optic reaction.



At the end of all this you should get a very high probability of beeing right in your conclusion as if this is an emerald or not.

By the way, a picture of the Rock and a closeup picture of the crystal would have helped a lot, the answer would have come faster and would have been shorter than this one....


Greetings from Austria,

Nikolaus

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 Post subject:
PostPosted: Thu Dec 11, 2008 6:45 pm 
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The emeralds I mine in NC are found on the contact zone between biotite mica and feldspar. If you see schrol you know you are getting close. You can find extremely small emeralds embedded in the feldspar but the bigger ones tend to grow off the surface of the feldspar directly into the biotite. You have to slowly peel back the biotite to find them. Here are a few examples of the host rock from there The only 2 decent matrix emerald spec. I have found I sold. All of these have very small green specks which are emerald(very very small hard to see in photo). Some good stuff has been found occasionally there. When my club had a dig there 2 weeks ago(posted under fieldtrips page) a friend found an emerald that was a 1/2 inch long and was eye clean. I was not there so I was skeptical about the stone being eyeclean but 30 people saw it and all agreed that it was one of the nicest crystals that have come from there and it was perfectly eyeclean. There are pics of it on my DRH forum.

The contact zone between the black and white si where you will find the good emerald crystals.
Image

Here is the biotite which you have to peel back slowly(after soaking)to find the crystals.
Image

Image

Here I found a pic of mine of an emerald from there in matrix.(friends stone) There is a schrol crystal near it too.
Image

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Last edited by Barrett on Fri Dec 12, 2008 3:45 pm, edited 1 time in total.

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 Post subject:
PostPosted: Thu Dec 11, 2008 9:06 pm 
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All of the above statements are good for id of emerald in the rough. You can identify it like any other mineral sample. One item also will be the hardness of the mineral (8). It should scratch quartz and corundum should scratch it. Streak should be white. And if the matrix is available, look for those associated minerals.
Image

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 Post subject:
PostPosted: Thu Dec 11, 2008 9:38 pm 
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hello sera

much good advice already.

i'll add something. emerald crystals nearly always have six sides - you see a hexagon shape when you look at them end on. there are other six sided green crystals- so this is just a starting point. if the crystal has 3 or 4 sides, it is not an emerald. also, the end of the emerald crystal is almost certainly flat - the emerald crystals do not have pointy ends like quartz crystals. lots of pixs of emerald rough here . look through them to get an idea of what rough emerald crystals look like and also the appearance of the various host rocks.

if you have spectroscope, light the specimen by either shining light through a crystal or by reflecting light off the surface of the crystal. examine the green light with the spectroscope. make sure you are looking at green light. emerald has a quite distinctive spectrum, which is most obvious in the stones that have a lot of chromium - these are a rich colour too. the emerald spectrum is here .

emeralds with a lot of chromium will look red, pink or brown under the chelsea filter. most african, indian and australian emeralds look green. i do not know the source of your rough.

an inexpensive pocket diffraction spectroscope will be fine for checking emerald spectrums.

you may be in a position to test the hardness of the crystals. emerald will always be scratched by sapphire and usually by spinel.

emerald will always scratch moonstone or other feldspars and usually quartz.

* be aware that there are unscrupulous individuals who "fake" rough emerald crystals and matrix rock, using a variety of materials, coloured resins and so on. i can post a pic or two if you like.

hope this info is of use and gets you started. good luck.


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 Post subject:
PostPosted: Fri Dec 12, 2008 1:03 pm 
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Great thread!

If you don't mind, I would love to see the photos of the fake rough.

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 Post subject:
PostPosted: Sun Dec 14, 2008 8:54 pm 
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hi rockcutter's wife

sorry to take a while to post these pix - i had to transfer 2 of them from some 35mm slides that i used to use in lectures - in the bad old days before powerpoint . because of this the quality is not as good as i would like but still acceptable, i think.

there are 3 pix of fake rough - corundum, emerald and ruby/ sapphire here

***just click on the thumbnails to see a bigger pic and accompanying description

cheers
agfa


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 Post subject:
PostPosted: Tue Dec 16, 2008 1:07 pm 
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wow..thank you, kinda of have to admire their craftsmanship, if only they used their skills for good...

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http://www.prettyrock.com/2012facetingcompetition.htm
Avon Breast Cancer Walk - Charlotte 2011 http://info.avonfoundation.org/goto/Beth


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 Post subject:
PostPosted: Thu Dec 18, 2008 8:47 am 
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Thank you ever so much for the indepth article on emerald rough id. Absolutely fantastic. I learnt so much already.

No wonder this is a great web site for any gemologist or gem hobbyist.

Cheers

Merry Christmas everyone and have a great holiday

sera

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 Post subject: Yet another no destructive test
PostPosted: Wed Oct 07, 2009 11:04 am 
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Folks,
here is another non-destructive test for emeralds that I have used for years. Place the rough on your computer flat bed scanner carefully, place a white cloth around the item. scan. the result if emerald should be red or pink. It is a simple test, as the scanner light is larger than the VISible range wave length....... winstone


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 Post subject:
PostPosted: Wed Oct 07, 2009 6:36 pm 
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Gosh ... I could have sworn I'd asked all the stupid question by now, but I guess not :P . Here are two more:

1. Does my hp psc 1210 all-in-one printer/scanner/copier qualify as a "flat-bed scanner"?

2. Are you checking the emerald as the light passes under it, or waiting for the color on the scanned page?

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 Post subject:
PostPosted: Wed Oct 07, 2009 7:51 pm 
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MoDo,

YEs your all in one qualifies.

I believe winstone is simply referring to the image obtained from the scan.

J-

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 Post subject: Re: Rough Emerald identification
PostPosted: Sat Apr 09, 2011 7:27 pm 
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I completely agree.

Two factors should although be kept in mind: mineral specimens of this size and quality are abundant. But having an an US pedigree, some collectors will still pay a premium over comparable material from other sources. My tip: Keep the piece if you enjoy it. Donate the piece to a local museum if you don´t like it. It´s definitely not one of the specimens, that would raise enough money to help you in your situation.

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