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Charcas - Pink Mineral
  
  Index -> What is it? - Where is it from?
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Linus




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PostPosted: Jan 16, 2020 16:01    Post subject: Charcas - Pink Mineral  

I recently found a couple flats of these cool calcites from Charcas. I recall that there was some controversy about what the pink drusy matrix of these specimens was - datolite, kutnohorite, chalcedony? any thoughts? By the way the calcite on the back of these is intensely fluorescent orange!


20200116_135057[1].jpg
 Mineral: Calcite
 Locality:
Aurora Mine, Charcas, Municipio Charcas, San Luis Potosí, Mexico
 Dimensions: 65 mm length
 Description:
 Viewed:  839 Time(s)

20200116_135057[1].jpg


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Tobi




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PostPosted: Jan 17, 2020 05:12    Post subject: Re: Charcas - Pink Mineral  

Hi Linus,

as long as I remember, these specimens from Aurora Mine with calcite on pale pink matrix have always been referred to as quartz. I know them as rather microcrystalline so I would say chalcedony could also be correct instead of quartz. But I'm neither a chemist nor a mineralogist, this is just what I always thought of as a collector.

Tobi
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Bob Harman




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PostPosted: Jan 17, 2020 10:16    Post subject: Re: Charcas - Pink Mineral  

A very close up of the photo shows the calcite itself to be on clear colorless druzy quartz, but near and along the rim of the specimen, there is also botryoidal pale pink ??? Maybe chalcedony. Bob
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Peter Megaw
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PostPosted: Jan 17, 2020 10:24    Post subject: Re: Charcas - Pink Mineral  

We have analyzed the pink material....it is datolite.
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Peter Megaw
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PostPosted: Jan 17, 2020 11:00    Post subject: Re: Charcas - Pink Mineral  

Here are two more examples. One is a stalactite of essentially pure datolite with only a few tiny calcites...the other is a miniature of the stalactitic datolite with small calcites sprinkled over the top.

This material came out in fair quantity about 10 years ago...especially the stuff Linus posted with the large blocky calcites...most of which were damaged. The stalactitic material was much scarcer, I have only seen a few tens of examples.

I am not sure these actually came from the Aurora...if anyone has solid provenance for them I would be delighted to hear



20200117_084101.jpg
 Mineral: Datolite
 Locality:
Charcas, Municipio Charcas, San Luis Potosí, Mexico
 Dimensions: 2 cm diameter, 7 cm long
 Description:
 Viewed:  646 Time(s)

20200117_084101.jpg



20200117_082742.jpg
 Mineral: datolite and calcite
 Locality:
Charcas, Municipio Charcas, San Luis Potosí, Mexico
 Dimensions: 4 cm tallk, 6 cm wide
 Description:
 Viewed:  645 Time(s)

20200117_082742.jpg



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Linus




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PostPosted: Jan 17, 2020 13:23    Post subject: Re: Charcas - Pink Mineral  

Hi thank you everyone! Basing my observations on Peter's comment, on very close examination, the "drusy" effect is caused by a second overgrowth of nearly clear datolite over the pink datolite base.
There were also a couple stalactitic datolites in these flats, one shown attached.



20200117_111135[1].jpg
 Mineral: Datolite
 Locality:
Charcas, Municipio Charcas, San Luis Potosí, Mexico
 Dimensions: 7cm long by 3 cm across base
 Description:
A stalactitic cluster of pink globular datolites on an interior core of brownish calcite (certain growth rings of the interior calcite are weakly fluorescent orange).
 Viewed:  606 Time(s)

20200117_111135[1].jpg


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Josele




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PostPosted: Jan 18, 2020 06:16    Post subject: Re: Charcas - Pink Mineral  

How misleading can be a mineral photo, last one could be confused with globular chalcedony from Mamuju, Indonesia!
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Tobi




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PostPosted: Jan 18, 2020 10:35    Post subject: Re: Charcas - Pink Mineral  

Josele wrote:
How misleading can be a mineral photo, last one could be confused with globular chalcedony from Mamuju, Indonesia!
That was exactly my first thought! Linus, are you sure this is datolite from Mexico and not chalcedony from Indonesia? ;-)
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Linus




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PostPosted: Jan 18, 2020 14:12    Post subject: Re: Charcas - Pink Mineral  

Hi Tobias, I can understand your doubts. For a number of years, I worked as a Geologist in the town of Charcas and purchased these direct from a miner, along with several nice danburites and nifontovites. Also, these stalactites have calcite cores which Im sure the grape chalcedony does not, and the pink globes are soft, hardness less than 6 (by scratch-point test).
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Linus




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PostPosted: Jan 18, 2020 15:09    Post subject: Re: Charcas - Pink Mineral  

I thought maybe a picture of the base of the stalactite would be helpful. base looks to be a cross-section of a vertical core of calcite, entirely surrounded by pink datolite globules... bands of this interior calcite are weakly SW flourescent orange, the outer pink mineral is not at all fluorescent under SW or LW.


20200118_130011[1].jpg
 Mineral: Calcite
 Locality:
Charcas, Municipio Charcas, San Luis Potosí, Mexico
 Dimensions: 3 cm long axis
 Description:
base of datolite stalctite showing calcite core
 Viewed:  442 Time(s)

20200118_130011[1].jpg


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Tobi




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PostPosted: Jan 19, 2020 03:10    Post subject: Re: Charcas - Pink Mineral  

Thank you for the explanation, Linus :-)

Regards
Tobi
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