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What is the correct name for this rock?
  
  Index -> What is it? - Where is it from?
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RicardoM




Joined: 28 Mar 2022
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Location: Mexico City

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PostPosted: Mar 28, 2022 17:58    Post subject: What is the correct name for this rock?  

Hi, I would like to know the correct name for this rock, for a time we are making lapidary with this material but still do not have the correct name.

Here people known it as chalcedony but I am in doubt.

Is harder than glass (scratch it), but softer than quartz, found along rhyolitic rocks in Queretaro state, México.
Vitreous luster, and irregular fracture.

Help is much appreciated.

Thanks in advance.

Ricardo



IMG_8892.JPG
 Mineral: unknown
 Locality:
Queretaro, Mexico
 Description:
 Viewed:  690 Time(s)

IMG_8892.JPG



IMG_8889.JPG
 Mineral: unknown
 Locality:
Queretaro, Mexico
 Description:
 Viewed:  688 Time(s)

IMG_8889.JPG


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SteveB




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PostPosted: Mar 28, 2022 18:24    Post subject: Re: What is the correct name for this rock?  

I’m thinking Gneiss, thats a guess NOT an identification
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alfredo
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PostPosted: Mar 29, 2022 01:23    Post subject: Re: What is the correct name for this rock?  

Looks like obsidian, and the locality fits too.
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Matt_Zukowski
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PostPosted: Mar 29, 2022 01:56    Post subject: Re: What is the correct name for this rock?  

I agree with Alfredo - it looks like a layered volcanic with obsidian and pumice.
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Bob Carnein




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PostPosted: Mar 29, 2022 10:46    Post subject: Re: What is the correct name for this rock?  

I'd call it a welded crystal-vitric tuff--essentially what Matt said.
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James Catmur
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PostPosted: Mar 30, 2022 03:23    Post subject: Re: What is the correct name for this rock?  

I never collected that sort of material near Queretaro, but obsidian and tuff make sense. I suspect 'chalcedony' is a way of not saying 'obsidian'!

Bob Carnein wrote:
I'd call it a welded crystal-vitric tuff--essentially what Matt said.
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Amir Akhavan




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PostPosted: Mar 30, 2022 08:10    Post subject: Re: What is the correct name for this rock?  

Obsidian with narrow bands of intense devitrification. The small dots are spots where the glass devitrified ("de-glassed", crystallized).
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Amir C. Akhavan, Hamburg, Germany
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