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[Robson Vieira]

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

[Amir Akhavan]

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.

[Riccardo Modanesi]

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.

[Robson Vieira]

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

[Bob Harman]

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