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The Illinois Fluorites with Calcite are chemically etched?
  
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R Saunders




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PostPosted: Jul 28, 2018 06:29    Post subject: The Illinois Fluorites with Calcite are chemically etched?  

Fluorite in calcite Hardin County, Illinois


Hardin County, Il.JPG
 Mineral: Fluorite
 Locality:
Illinois, USA
 Description:
Southern Illinois
 Viewed:  4162 Time(s)

Hardin County, Il.JPG


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R Saunders




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PostPosted: Jul 29, 2018 04:56    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

I have looked at a few pieces of Fluorites at a Michigan show. Of the rough pieces that I have from Illinois, am I correct to assume. that all the cube or smooth sided shapes are cut or chemically etched into the pieces? A dealer said that his are that way after all the matrix has been removed. I doubted that. Thanks
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Bob Harman




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PostPosted: Jul 29, 2018 06:57    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

R SAUNDERS,

Not exactly understanding what your questions are so let me try to explain to you in general terms.
With reference to your pictured example, it is a piece of fluorite and calcite, probably from close to the edge of the ore body and almost certainly from the Harris Creek District of the Illinois fluorite district. These kind of pieces were commonly collected about 15 - 20 years ago, shortly after the mines closed.
Your piece shows no intact fluorite crystals on the surface, just broken and cleaved portions of fluorite intimately mixed with the calcite. If the calcite were removed with vinegar or HCl soaking, a few cleavage planes of fluorite might be exposed, but almost certainly no fully intact fluorite crystals would be exposed. In addition, your piece would fall apart into multiple pieces. I would NOT try to remove the calcite as you will then only be left with multiple small pieces of fluorite with no intact crystals.

With appropriate specimens, dealers and specimen preparers evaluate quality fluorite specimens and often do remove unwanted calcite to better expose the fluorite crystals and improve their specimens, but your example would not be one that could be improved. BOB
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R Saunders




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PostPosted: Jul 29, 2018 07:59    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

Bob Harman, Thank you for the information. My in law's have property in the area and have gone on the 9 day horse rides for many years. The piece shown may be older than 15-20 years but not sure. I asked in reference as to the pieces shown here having cubed or squared shapes. Why do they do acid etching of them?
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Bob Harman




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PostPosted: Jul 29, 2018 09:06    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

The fluorite is acid etched to better expose it and clean off any thin carbonate coating in appropriate specimens. The fluorite is unaffected by the vinegar or acid so its color and luster may be improved. BOB
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PostPosted: Jul 29, 2018 09:16    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

The cubes and square edges are totally natural, and the result of crystal growth. So many of the specimens you see are exactly as they were when they were removed from the mine. In some cases they may have been chemically treated to improve them, but not to etch the fluorite.
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lluis




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PostPosted: Jul 29, 2018 11:19    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

Bob Harman wrote:
The fluorite is acid etched to better expose it and clean off any thin carbonate coating in appropriate specimens. The fluorite is unaffected by the vinegar or acid so its color and luster may be improved. BOB


Hi, Bob

Fluorhidric acid with calcium carbonate would generate calcium fluoride, that is fluorite....
It would make a mess and make specimen just coated with a blanket of white dust (that could be very attached, besides....).
Say if not to the textile mills that use a fluorhidric derivative to complex iron and avoid troubles... If no calcium there, no trouble. If any, as usual, specially with cotton from China, they get a "nice" nightmare....

On the other side, fluorite in concentrated fluorhidric acid dissolves a little, with possibility to having frosted surfaces.....
As in all, you should know before what you do.... (just trial and experience.... and several specimens to junk.... :-( )

With best wishes

Lluís
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R Saunders




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PostPosted: Jul 29, 2018 11:22    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

Here is another piece. Soaked in Iron Out. app. 30 minutes. Removed a lot of crud.


P1000183.jpg
 Mineral: Fluorite rough
 Description:
 Viewed:  4000 Time(s)

P1000183.jpg


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R Saunders




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PostPosted: Jul 29, 2018 11:23    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

rough colors


P1000185.jpg
 Mineral: more
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P1000185.jpg


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R Saunders




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PostPosted: Jul 29, 2018 11:26    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

Could there be anything to improve? Leaving natural.


P1000184.jpg
 Mineral: nice shape.
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P1000184.jpg


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Kevin Schofield




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PostPosted: Jul 29, 2018 11:37    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

lluis wrote:
Bob Harman wrote:
The fluorite is acid etched to better expose it and clean off any thin carbonate coating in appropriate specimens. The fluorite is unaffected by the vinegar or acid so its color and luster may be improved. BOB


Hi, Bob

Fluorhidric acid with calcium carbonate would generate calcium fluoride, that is fluorite....
It would make a mess and make specimen just coated with a blanket of white dust (that could be very attached, besides....).
Say if not to the textile mills that use a fluorhidric derivative to complex iron and avoid troubles... If no calcium there, no trouble. If any, as usual, specially with cotton from China, they get a "nice" nightmare....

On the other side, fluorite in concentrated fluorhidric acid dissolves a little, with possibility to having frosted surfaces.....
As in all, you should know before what you do.... (just trial and experience.... and several specimens to junk.... :-( )

With best wishes

Lluís


I'm not sure that we should be encouraging innocent members of the general public to mess about with hydrofluoric acid in these pages...a thoroughly evil substance very definitely best left to the professionals with fume cabinets, respirators and full-body rubber suits!

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Veni, Vidi, Emi
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lluis




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PostPosted: Jul 29, 2018 12:08    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

And with a flask of calcium alginate near, if any trouble happens...!!!

I am chemist, and the few products that scare me, one is Fluorhidric. The other, diazald (this one, nothing to do with minerals....)

Fluorhidric should not be used, as Kevin says, unless you have all the needed... and have experience. A burning with fluorhidric is a very bad thing...

With best wishes

Lluís
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Bob Harman




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PostPosted: Jul 29, 2018 12:34    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

Lluis, With regards to etching calcite and other carbonates on mineral specimens, I assume some basic knowledge. "Acid" basically means vinegar, acetic acid, and dilute HCl, and no other acids. If people in other parts of the world don't assume some basic knowledge and have to post every other imaginable detail, then much of my time here is a waste.

And for Saunders other specimens. They are typical of the edge of the ore body in the Harris Creek District. I personally think nothing can be done to really improve them. Etching off the limestone and any calcite will just leave many small pieces of fluorite and a bit of sphalerite (if present). BOB
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lluis




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PostPosted: Jul 29, 2018 13:22    Post subject: Re: The Illinois Fluorites with Calcite are chemically etched?  

Hi, Bob

What you think and said (in which I generally would agree, adding some other acids... Advantages to be chemist,.apart to be bad seen by all... :-) ), and I falsely read was not same...
My brain placed Fluorite as fluorhidric... But fluorhidric is an acid.... Nasty for health, weak and so. But and acid, with all letters and properties
Anyway, thinking that all people has the basic knowledge you have, well, sometimes is far bold...
Anyone of us knows what he knows,
More specific, not a waste of time, simply more sure...

With best wishes

Lluís
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