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Posted in response to Re: Re: Re: Re: Anyone kind enough to evaluate this rough gem from Edward on December 11, 2007 at 14:21:08:

Re: Re: Re: Re: Re: Anyone kind enough to evaluate this rough gem

Hi again Ed,

Well, the darker areas showing in your pictures are intriguing. When you hold the stone up to a light source, can you see any light through them or are they opaque?

"Faceting quality" is one of those somewhat debatable terms for which there are no universally accepted criteria. Some less-than-discriminating rough dealers seem to conveniently confuse and employ the terms "faceting quality" and "facetable" interchangeably. [sigh] When you get right down to it, you can facet just about anything using diamond abrasives, even other diamonds - and of course driveway gravel too. While the gravel in my driveway may be facetable, most faceters would not consider it to be "faceting quality" limestone. :)

Generally speaking, the more transparent and free of cracks, inclusions and other defects a mineral crystal is, the more it approaches an ideal "faceting quality". There are additional factors at play such as size and shape, and of course color is a big one as well.

"Eye clean" may be a little more useful term for describing quality faceting material. "Eye clean" means that whatever inclusions and other imperfections present in the material are sufficiently minute that they will not be visible to the unaided eye in a finished stone. This is not to say that you cannot facet pleasing stones from less than eye clean material, but generally speaking, the "cleaner" the material the higher its quality is regarded to be. If you can inspect it under a 10x loupe and still see no imperfections, it is *very* clean - a diamond that clean is considered flawless for grading purposes.

Emerald is particularly nasty stuff regarding inclusions, with even eye clean emeralds being rather far and few between. When I first began faceting, I was just chomping at the bit to cut an emerald. I finally acquired a crystal I deemed suitable for a first shot at an emerald, which I would describe as "highly included" - but I wanted to cut an emerald so badly I decided to give it a go. I had not even finished cutting the pavilion when the stone broke badly, having become fatally weakened during the faceting process by the removal of material that had been holding it together...

That was the first and to date the only emerald I have tried cutting, deciding early on that I had better things to do with my money and time than cut less than facet quality rough. Bottom line is I can afford facet quality amethyst, garnet and other less than precious stones, but not facet quality emerald. [big sigh]

It would probably be for the best if you do not chip apart your stone looking for "facet quality" areas inside it. If any do exist, you are very likely to ruin them in the process. That is an exploration that is better conducted with a rock saw or grinder than a hammer, particularly so by those who are not expert in the use of a cobbing hammer and bed.

Keep on Rock'n!

From Bob Keller - December 11, 2007 at 15:29:27

Message: 65689

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Bob Keller