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 Post subject: Crystalline structure
PostPosted: Mon Dec 10, 2012 9:34 pm 
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Several of the gemology books in my library show drawings and
go into considerable detail about gem crystals, but no mention
of any equipment that reveals such structures. Is it super high-tec
or are there simpler devices that can be used to see internal
crystalline structure of a faceted stone?


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 Post subject: Re: Crystalline structure
PostPosted: Tue Dec 11, 2012 10:06 am 
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Commonly you decide the crystal structure via external signs as the number of prism faces, terminations etc. You could use a microscope or via other gemological tools use the optical properties of the mineral as aid, if the stone for instance is cut

The microscope is not a especially advanced instrument but as with all gemological instruments one need proper training for it to be of use. There is no real "Tricorder" for mineral's crystallographic properties which in most cases has to be determined with experience and knowledge or with help from mineralogical tables if one does not know by heart.

So the simple answer is, no there is no easy way to determine this without proper training and/or experience.

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 Post subject: Re: Crystalline structure
PostPosted: Wed Dec 12, 2012 1:08 am 
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Thank you,Ms. Forsberg - for your response to my query.
Would you be so kind as to expand upon your comments
with more detail and recommendations? Thanks, in advance.


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 Post subject: Re: Crystalline structure
PostPosted: Wed Dec 12, 2012 11:35 am 
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KRO wrote:
Thank you,Ms. Forsberg


he's actually a Mr............... :wink:

ciao
alberto

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 Post subject: Re: Crystalline structure
PostPosted: Wed Dec 12, 2012 3:23 pm 
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KRO Some crystal habits are easily recognisable so some gem materials can indeed be ID'd from just looking at the crystal shape. Quartz for example comes in a very recognizable shape when the crystals are well defined and the terminations can be seen. Unfortunately most / many gems come in rough tumbled shapes and crystal form and habit may be difficult to see.

Try to google crystal systems. you will learn that there are seven of them (Six if you use the Merry kin system). learn what shapes and terminations are common to each system, then to each gem type you are interested in. Then learn each systems essential symmetry, whether there is likely to be incipient cleavage in particular stones...etc etc etc the more information you can learn the more chance there is of recognising a particular gem crystal

After you have a good understanding of the above then practice by looking at as many well formed crystals as you can. It will soon develop into an ability to make a 'good guess' when you see a crystal shape. It's about learning the angles and shapes of the crystals. No equipment required Though loupes, microscope etc can make things easier sometimes. The only thing which might help imho in the way of equipment would be a digital protractor for measuring angles between faces.

Hope this helps


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 Post subject: Re: Crystalline structure
PostPosted: Wed Dec 12, 2012 6:06 pm 
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http://gemologyonline.com/crystal_systems.html


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 Post subject: Re: Crystalline structure
PostPosted: Sat Dec 15, 2012 2:44 pm 
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I thought the initial question was regarding finding crystal structure in cut stones only. Guess the answers cover more than that topic. Hope you are satisfied with them KRO.

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 Post subject: Re: Crystalline structure
PostPosted: Sat Dec 15, 2012 4:00 pm 
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Thank you, MR. Conny Forsberg, and others for your responses.
It seems to me now that once a stone has been faceted, its
in-the-rough crystal structure is no longer observable by eye nor
via simple gemological instruments, regardless of one's gemolog-
ical knowledge or experience, and that x-ray equipment is needed.


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 Post subject: Re: Crystalline structure
PostPosted: Sat Dec 15, 2012 4:14 pm 
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Actually in many cases knowledge about mineralogy and cutting in combination with gemological microscopy can reveal the crystallographic orientation. In the same way use of a polariscope, dicroscope and/or refractometer can do the same. But you need proper training to be able to interpret what you see.

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