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| Search found 23 matches |
| Author | Message |
|---|---|
 Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
 Forum: Minerals and Mineralogy Posted: Apr 09, 2025 11:50 Subject: Re: cristobalite vs chalcedony in thin section |
| Thanks everybody for feedback and suggestions.
Let me add some more pictures of chalcedony flowers growing inside gypsum cristals from the same evaporite formation. Incidentally, Marco, it seems tha ... |
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| Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
Forum: Minerals and Mineralogy Posted: Apr 08, 2025 11:13 Subject: Re: cristobalite vs chalcedony in thin section |
| Hi Daniel,
From the hand sample the chalcedony is spherical and I don't see any faces. From the last photo you can see chalcedony filling a cavity inside a gypsum crystal, but I still don't see any f ... |
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| Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
Forum: Minerals and Mineralogy Posted: Apr 08, 2025 09:34 Subject: Re: cristobalite vs chalcedony in thin section |
| Robert Folk taught that length-slow chalcedony was indicative of formation under evaporitic or sulfate rich conditions. If you have a gyp plate you could check that out
Thanks, Yes I did. Unfortu ... |
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| Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
Forum: Minerals and Mineralogy Posted: Apr 08, 2025 09:27 Subject: Re: cristobalite vs chalcedony in thin section |
| Sorry to be unclear. What I see is that silica (chalcedony) takes the place of former gypsum lenses, growing from the faces inwards. I agree that the likely mechanisme is coupled dissolution-precipita ... | |
| Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
Forum: Minerals and Mineralogy Posted: Apr 08, 2025 06:53 Subject: Re: cristobalite vs chalcedony in thin section |
| My impression is that it is all chalcedony. Chalcedony is a fibrous silica polymer so the structure you see in thin section looks very similar to it. Cristobalite is stable over 1470 C, Therefore it i ... | |
| Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
Forum: Minerals and Mineralogy Posted: Apr 08, 2025 04:07 Subject: Re: cristobalite vs chalcedony in thin section |
| Cristobalite is high T mineral. All supposed cristobalite spherulites are other silica phase.
So, no way to identify the textural pattern ? Here is a macro view of the spherulites |
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| Topic: cristobalite vs chalcedony in thin section |
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| Daniel Garcia Replies: 16 Views: 3833 |
Forum: Minerals and Mineralogy Posted: Apr 08, 2025 03:34 Subject: cristobalite vs chalcedony in thin section |
| Dear all
I'm trying to document a silicification event in Oligocene evaporites near Narbonne (France) The host rock is gypsiferous, with some diagenetic native sulfur. Silicification occurs sporad ... |
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| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 31, 2022 01:02 Subject: Re: Pseudomorph chemistry - (40) |
| Hi everybody,
Thanks, Cesar, for this expanded picture of the stability relationships in the H2O O2 CO2 SO4 CuO system. I have two questions and a suggestion. (1) Which is the thermodynamic databa ... |
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| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 29, 2022 08:15 Subject: Re: Pseudomorph chemistry - (40) |
| Thanks Roger, for this nice "macro" case.
It seems to me that in the dotted area of your last picture, the termination of the malachite cristals simply mimic the striated outer shape of the ... |
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| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 28, 2022 13:43 Subject: Re: Pseudomorph chemistry - (40) |
| Thanks Roger
Here is the same view under normal light. Azurite is still blue. It seems to be one single crystal, that inherits its shape from the pore geometry. Some other pores in the same sectio ... |
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| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 28, 2022 05:45 Subject: Re: Pseudomorph chemistry - (40) |
| Here is a thin section of a porous rock (mostly quartz) with pore filling azurite (blue) being partly converted to malachite (fibers). Looks similar to some of the Tsumeb specimens previously posted o ... | |
| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 20, 2022 11:11 Subject: Re: Pseudomorph chemistry - (40) |
| Hello Daniel
I am obviously interested in additional information. Can you give your opinion on the azurite – malachite transformation? I assume that the phenomenon of pseudomorphosis is more common ... |
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| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 18, 2022 14:42 Subject: Re: Pseudomorph chemistry - (40) |
| Sorry, but Im not currently able to attach a pdf file to my personal messages.... | |
| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 18, 2022 03:42 Subject: Re: Pseudomorph chemistry - (40) |
| Hello Daniel
I am obviously interested in additional information. Can you give your opinion on the azurite – malachite transformation? I assume that the phenomenon of pseudomorphosis is more common ... |
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| Topic: Pseudomorph chemistry - (40) |
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| Daniel Garcia Replies: 28 Views: 45858 |
Forum: Featured Columns of FMF Posted: Aug 18, 2022 02:04 Subject: Re: Pseudomorph chemistry - (40) |
| "Superb reference"
Indeed, one of my top ten geoscience papers. A copy is available upon request by MP. Pseudomorphism, and more generally mineral replacement is a fascinating topic. ... |
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