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"Frosted patterns" on the faces of Quartz
  
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Reef




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PostPosted: Nov 27, 2017 05:45    Post subject: "Frosted patterns" on the faces of Quartz  

I would call this dendritic growth. But it is believed that quartz can not have it.
The sizes of the samples are mainly up to ~ 15 mm.
Locality: Alatau, Bashkortostan Republic, Southern Urals, Urals Region, Russia



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Niels Brouwer




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PostPosted: Nov 27, 2017 08:39    Post subject: Re: "Frosted patterns" on the faces of Quartz  

It doesn't really look like dendritic growth to me, as far as I can tell from these images. It reminds me more of the cracks you see for example in mud. I suspect a more likely explanation for the patterns on those crystals would be some sort of coating that covered the face of the quartz during its development. It looks like the coating developed cracks through which the quartz could continue to grow, whereas the remaining areas of coating inhibited the growth, resulting in the lower areas on the faces.
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Bob Harman




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PostPosted: Nov 27, 2017 09:13    Post subject: Re: "Frosted patterns" on the faces of Quartz  

I believe you can see this type of very superficial surface change in many types of crystals, whether they be resistant and stout, like quartz, or less resistant and fragile like calcite and fluorite. I believe this is a type of slow superficial surface etching with resorption. Remember, these crystals have existed for many millennia and been subjected to ambient fluids for the same time frame. Very slow surface etching and resorption might preferentially occur on some of the crystal surfaces. Much more rapid changes occur with other minerals such as calcite or fluorite leading to corrosion with some interesting etched forms. BOB
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Pierre Joubert




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PostPosted: Nov 27, 2017 10:42    Post subject: Re: "Frosted patterns" on the faces of Quartz  

I believe these crystals formed in association with another mineral species that 'weathered away, leaving these beautiful markings. What the other mineral was can possibly be established by studying the direct environment.
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PostPosted: Nov 27, 2017 10:49    Post subject: Re: "Frosted patterns" on the faces of Quartz  

I would like to add that the edges of these patterns will most likely be sharp and not rounded. If one made a cast of this pattern, it will help a lot to understand the other 'weathered' mineral/s.
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John Betts




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PostPosted: Nov 27, 2017 11:30    Post subject: Re: "Frosted patterns" on the faces of Quartz  

I think the quartz is twinned following the Dauphiné law and that is preferential etching of one of the quartz "hands" (i.e. left-hand quartz or right-hand quartz was etched, the other not etched.)
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Pierre Joubert




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PostPosted: Nov 27, 2017 12:54    Post subject: Re: "Frosted patterns" on the faces of Quartz  

John Betts wrote:
I think the quartz is twinned following the Dauphiné law and that is preferential etching of one of the quartz "hands" (i.e. left-hand quartz or right-hand quartz was etched, the other not etched.)


It seems that the term 'edging' is a very debatable topic. I find the following extract from William C van Laer very interesting:
'Often what is referred to as "etched" crystals are just growth--reverse growth phases repeated, as the line between stability and instability is crossed again and again (a good example of this is the spessartine garnets found recently in Brazil, along with those found elsewhere in pegmatite pockets like the Little Three Mine in California).'

https://www.mindat.org/forum.php?read,6,269694,269818

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PostPosted: Nov 27, 2017 12:59    Post subject: Re: "Frosted patterns" on the faces of Quartz  

I do not know how this is formed, but interesting and beautiful. In my opinion there is no etching here. Whims of skeletal growth. Host rocks: calcareous sandstone, marl, calcite, dolomite. The veins themselves: calcite and a little quartz.


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Reef




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PostPosted: Nov 30, 2017 05:23    Post subject: Re: "Frosted patterns" on the faces of Quartz  

A request, who has similar samples with a "dendritic" pattern, publish a photo.
A few more photos.



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DSCI60331.jpg
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 Dimensions: 20x11mm
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Pierre Joubert




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PostPosted: Nov 30, 2017 06:46    Post subject: Re: "Frosted patterns" on the faces of Quartz  

Most unusual and quite unique!
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