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Polish Chert
https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=56&t=22685
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Author:  Barbra Voltaire, FGG [ Mon May 09, 2016 7:55 pm ]
Post subject:  Polish Chert

A friend recently brought this magnificent CHERT slice to brunch. It is over 12" long.
I have never seen anything like it. Totally opaque.

Image

It was purchased in Tucson last February. Sold as Polished chert nodule from Jurassic limestone, Kielce, Poland

Author:  Stephen Challener [ Mon May 09, 2016 7:59 pm ]
Post subject:  Re: Polish Chert

Usually marketed as polish flint, it's a really spectacular material. It takes one hell of a high polish too, and the darker bands are a bit translucent. Other locales produce banded flint but I've never seen any like the Polish material.

Author:  Barbra Voltaire, FGG [ Mon May 09, 2016 9:09 pm ]
Post subject:  Re: Polish Chert

Do you happen to have any specific information on this formation?
I presume voids in limestone filled by siliceous H2O.....but ending up with chert, not agate?
That's................unexpected, no?

Some crazy tectonic action?

Author:  Stephen Challener [ Mon May 09, 2016 10:10 pm ]
Post subject:  Re: Polish Chert

Alas, I'm afraid it's actually pretty typical to get chert rather than agate in that context. There's some debate over the exact mechanisms involved as I understand it, but chalk and limestone are the typical hosts for flint/chert nodules. The patterning is in all likelihood a spectacular example of liesegang banding developed during or after the initial nodule formation.

Author:  Barbra Voltaire, FGG [ Mon May 09, 2016 10:20 pm ]
Post subject:  Re: Polish Chert

Kewl info.

Author:  dchallener [ Tue May 10, 2016 9:15 pm ]
Post subject:  Re: Polish Chert

There is a nice one just ending on ebay - no bids - here:
http://www.ebay.com/itm/TCR-POLISH-FLIN ... SwKfVXKpzf

I don't know anything about the seller, but it is a nice picture.

Author:  Barbra Voltaire, FGG [ Wed May 11, 2016 12:20 am ]
Post subject:  Re: Polish Chert

Thanks. I just put a $9 bid on the slab.
Yep, it's cracked and not even close to the awesomeness of Norman Mahan's slab......but I am merely a minion in his shadow. 8)

Author:  dchallener [ Wed May 11, 2016 7:44 pm ]
Post subject:  Re: Polish Chert

Hope you get it - it makes truly nice cabs. I picked one up at a small rock shop in California years ago and it gave me some really nice cabs.

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