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thin section rhyolithic tuff, srp
  
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FlashFIre90




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PostPosted: Oct 19, 2018 06:06    Post subject: thin section rhyolithic tuff, srp  

Hey there, i have a thin section of rhyolitc tuffs and would like to know which kind of minerals are included.

I think its feldspar, but what is the brown stuff around it?



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FlashFIre90




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PostPosted: Oct 19, 2018 06:09    Post subject: Re: thin section rhyolithic tuff, srp  

polarized


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FlashFIre90




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PostPosted: Oct 19, 2018 06:10    Post subject: Re: thin section rhyolithic tuff, srp  

one more , polarized:)


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FlashFIre90




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PostPosted: Oct 19, 2018 06:11    Post subject: Re: thin section rhyolithic tuff, srp  

and normal picture, whats the green mineral, which is multicoloured in polarized pic? :)


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Peter Megaw
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PostPosted: Oct 19, 2018 06:58    Post subject: Re: thin section rhyolithic tuff, srp  

The clot looks like a xenolith of a mafic igneous rock composed of elongate plagioclase laths and pyroxenes.

The highly birefringent grain is probably a zircon

The shard textures are spectacular

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Peter Megaw
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PostPosted: Oct 19, 2018 07:39    Post subject: Re: thin section rhyolithic tuff, srp  

plenty of opaques too...probably magnetite
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Bob Carnein




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PostPosted: Oct 19, 2018 10:10    Post subject: Re: thin section rhyolithic tuff, srp  

I agree with Peter. The major component appears to be welded glass shards (not feldspars), which are isotropic (non birefringent). Based on your photos, I'd call this a welded vitric tuff with minor lithic and crystal (possibly sanidine) components.
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