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Faden Quartz Crystals - (26)
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Pierre Joubert




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PostPosted: Apr 13, 2017 13:02    Post subject: Re: Faden Quartz Crystals - (26)  

Tobi wrote:
Pierre Joubert wrote:
Here are a few very small samples from the Western Cape.
Mineral: Quartz
Locality:Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
Really nice small faden quartzes, Pierre. Is it the lighting or are they pale yellow - which would make them natural citrine and thus even more interesting and desirable ...?


No Tobi, Sorry, but they are anything but citrine :-) I wish! It must be the lighting.

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Tobi




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PostPosted: Apr 14, 2017 01:40    Post subject: Re: Faden Quartz Crystals - (26)  

Pierre Joubert wrote:
Tobi wrote:
Really nice small faden quartzes, Pierre. Is it the lighting or are they pale yellow - which would make them natural citrine and thus even more interesting and desirable ...?
No Tobi, Sorry, but they are anything but citrine :-) I wish! It must be the lighting.
Don't worry, they are really good even without colour!
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Jordi Fabre
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PostPosted: Dec 03, 2017 11:29    Post subject: Faden Quartz Crystals - (26) - Pendulum's Swing  

In a kind of "pendulum's swing" this thread has come and gone. It was created here and it was picked up by the adorable mini-magazine MiniBul of the Belgian Mineralogical Society A.G.A.B. that picked it up and expanded it into an article, and now it comes back to FMF thanks to the permanent kindness of Mr. Roger Warin that has authorized us to reproduce it here and he even translated it to English language through his friend Christian Servais, PhD at the University of Liège.
I recommend to all the FMFers to read it and then return to impel the pendulum, this time (and again) from FMF ;-)

This is the introduction to this swing pendulum that Mr. Warin has done:

When we admire the minerals, we can’t prevent us to dream. The human mind wanders... But where do these remarkable crystals come from? Even the most modest specimens ask questions.
The pearls of the collections are often secreted by hydrothermal waters. But what is nourishing this liquid? Unusual temperatures and pressures prevail in this environment. All notions change. The rock crystals of the Alps inspire purity. Their origin was sometimes singular. They are born in hydrothermal conditions. I was led to generalize these origins. In both cases, the hydrothermal medium was relatively pure silica. The only differences are the pressures and temperatures of the hydrothermal system.
Amateur of meteorites, I also studied the Libyan Desert Glass and all these reflections have allowed me to suggest the important role of silica SiO2 "solutions" feeding crystals of quartz below 450 °C and of cristobalite and other allotropes dispersed in Libyan Desert Glass above 1500 °C.
Is in this spirit that I took the description of the growth of the various Faden Quartz.

To see it click on this link or in the image:


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Frei Hans




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PostPosted: Dec 14, 2017 12:18    Post subject: Re: Faden Quartz Crystals - (26)  

In this faden quartz from Pakistan the faden seems to be broken. What happened?


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Roger Warin




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PostPosted: Dec 15, 2017 06:43    Post subject: Re: Faden Quartz Crystals - (26)  

I see a shear that followed the first flash crystallization of the soul. As the gel is viscous, it would have kept in memory the previous situation prior to calm and normal crystallization in a second step.
A very slight sliding of the walls relative to each other (a few hundred microns < 1 cm) caused this fracture of the soul just after its precipitation. The ends are then welded. In a dense gel, there is no reason for the pieces of the soul to fall while in a liquid it would be immediate.
Your observation therefore supports my hypothesis that the hydrothermal medium is a viscous gel of SiO2.
Thank you for your comment.
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marco campos-venuti




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PostPosted: Dec 15, 2017 11:28    Post subject: Re: Faden Quartz Crystals - (26)  

Hi Roger,
I consider we are at the same side of the theories, as anti-official. But something in your discussion sounds strange to me.
A gel is a solid and for that reason can't have viscosity that means deformation. Gel cracks as a solid, is elastic, but no plastic. Inside silica gel, quartz can't exist and a silica polymer is stable, the chalcedony.
In my mind the formation of the polymer filament is inside a gel. The quartz growths in a second time in a dilute solution as epitactic crystallization over the polymer filament. Such a simple!
marco
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