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Is this "dehydrated" opal?
  
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Robson Vieira




Joined: 05 Jan 2017
Posts: 28
Location: São Paulo

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PostPosted: Jan 07, 2020 17:43    Post subject: Is this "dehydrated" opal?  

Hi folks. I have a chalcedony sample and I would like to clarify the identifcation. Here in Brazil it is common to refer this material as dehydrated opal. I refer to the white dull portion of the sample and not the translucent part. It has the luster of kaolinite. It seems porcelain as well, just for comparison.
My question is: is there such mineral? Is the dehydrated opal name just a fake name?
And if the name is right, how does the dehydration process really occur?

Thanks



20200107_191303.jpg
 Mineral: Quartz (variety chalcedony) ?
 Description:
North São Paulo State
6 cm x 4 cm
 Viewed:  3928 Time(s)

20200107_191303.jpg



20200107_191241.jpg
 Mineral: Quartz (variety chalcedony) ?
 Description:
North São Paulo State
6 cm x 4 cm
 Viewed:  3922 Time(s)

20200107_191241.jpg



20200107_191201.jpg
 Mineral: Quartz (variety chalcedony) ?
 Description:
North São Paulo State
6 cm x 4 cm
 Viewed:  3925 Time(s)

20200107_191201.jpg


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Amir Akhavan




Joined: 01 Dec 2009
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Location: Hamburg

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PostPosted: Jan 10, 2020 19:44    Post subject: Re: Is this "dehydrated" opal?  

This is almost certainly a weathered agate.
Agates can alter to a white, sometimes porcelain-like and sometimes even crumbly or powder-like material which is composed of quartz.

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Amir C. Akhavan, Hamburg, Germany
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Riccardo Modanesi




Joined: 07 Nov 2011
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PostPosted: Jan 11, 2020 06:23    Post subject: Re: Is this "dehydrated" opal?  

Hi to everybody!
I can confirm: weathered agate. I found plenty of this kind in Idar-Oberstein and surrounding village; it's a historical agate and amethyst deposit!
Greetings from Italy by Riccardo.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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Robson Vieira




Joined: 05 Jan 2017
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PostPosted: Jan 11, 2020 07:24    Post subject: Re: Is this "dehydrated" opal?  

Amazing!! Many thanks friends Amir and Ricardo. Regards from Brazil.
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Bob Harman




Joined: 06 Nov 2015
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PostPosted: Jan 11, 2020 09:23    Post subject: Re: Is this "dehydrated" opal?  

I agree, an extreme example of a dried out chalcedony nodule or agate.

The precise point of my thread from May 13, 2019 posting in the "Conserving and Mineral Preparation" section. This posted example is the reason I now keep my freshly collected chalcedony specimens hydrated by storing them under water. Bob
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