FMF - Friends of Minerals Forum, discussion and message board

[Pierre Joubert]

[Tobi]

[Jordi Fabre]

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:

[Frei Hans]

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

[Roger Warin]

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.

[marco campos-venuti]

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

[Frei Hans]

Thank you for explanation of my comment.
Some thoughts about Faden Quartz:
Pictures and videos of the seldom seen needle ice
(e.g. https://wagnerger.ch/daten/haareis4.pdf )
link normalized by FMF
promoted me to new thoughts about the origin of fadenquartz. The needle ice is growing from the bottom, sprouting up like a plant. Not only ice is growing in this kind, but also Zn-whiskers, feared to damages in electric devices. ( e.g. How do whiskers grow...E,Chason et.al.). Actually, quartz too, can solidify in this manner. (I.Sunagawa et.al. Journal of Crystal Growth 2005 276 p. 663-673).

First, a whisker, better to say a column of SiO2 grows out from the wall of a cavity in the modality of an ice column, Whether it is a crystal or a chalcedony, who knows. If the conditions turn to crystalisation requirements,a clear quartz grows over the column containing it as faden in his body. At the point, the column comes in to being, many flows are generated and inclusions are created in the column. A special reason to create flows can lead to a chain of inclusions in a line, as shown in picture 1,) If the column would be chalcedony, the polycrystalline structure must change to monocrystalline, because at the end ,the thread definitely is a part of the crystal and no more polycrystalline. ( Description to "quartz faden 3a.jpg" Pete Richards in this toplc. also to see, the line inclusions) In a column grown as crystal the crystal structure would be the same over the full length of the thread, and therefor in the overgrown quartz. The question is: How and way a column can grow from a solid surface?

[Roger Warin]

Hi Frei Hans,
The genesis of the sample you bring is explainable with my theory as well as the succession of events that gave birth to this configuration.
Roger.

[Roger Warin]

Hi Marco,
Yes, we are on the same and sunny side of the hypothesis. I think so ... But there are nuances.
What is the nature of silica gel? A solid phase? No. It is not solid "silicagel" industrially prepared, water-hungry material.

For me, silica gel is a very viscous fluid. Hydrothermal water is supersaturated with silica to the point that internal 3-dimensional polymerization can occur by formation of siloxane Si-O-Si bridges.
Bulk polymerization or mass polymerization is carried out by high temperatures and pressures.

H2O water molecules are compatible with this medium, by internal bonds including "hydrogen bridges". So, all the water molecules aren’t free. The system is aggregated without being solid because the disorder is high. The temperature must be above 300°C for the water to begin to escape.

I was brought to this notion by generalization of a similar phenomenon that produces Libyan Desert Glass, but at very high temperatures (>1800°C). This is another problem about which I have already written. To put it another way, I am also in opposition in this case with the official theory that involves the fall of a comet (or a meteorite, although there are no terrestrial residues). This last theory on the terrestrial endogenous origin of a 98% silica-rich hydrothermal phase LDG, I owe it to the German geologist Norbert Brugge: The non-impact origin of the Libyan Desert Glass (LDG). http(.)//www(.)b14643(.)de/Sahara/LDG/
You will find in this article one of my pictures showing cristobalite included in the LDG. Now, my personal contribution is to better specify the properties of this aqueous phase of pure silica: the hydrothermal liquid.

Let's go back to the Frei Hans’s specimen and to the question of the day. A final micro-shear breaks the tenuous ‘thread” (Faden) of crystallized quartz within the uncrystallized, viscous gel. This very thin crystalline column (with bubbles planes included), broken at places, moves as a group in the volume of the gel from which it follows the global movement. This translatory shock occurs just after the formation of the soul and before normal alpha-quartz crystallization resumes. Therefore, this (later) whole group of macro crystals did not incur the faden deformation/breakage.
To make it clearer, the soul is in fact a zone of silica gel which differs from the rest by the existence of an ordered trace of quartz, crystalline but without defined faces, which penetrates the disordered and gelled mass. This crystalline column is not delimited by distinct faces. We see this soul by the presence of transverse planes in which are the fluid inclusions (water, gas).
Roger.

[Harjo]

I have the impression that your theory, Roger, is not at all far off from the commonly accepted theory like described in Rykart, or in other literature for that matter.
Maybe the cracking and re-healing process has taken on a too literal explanation over the years, whereas it should be interpreted solely as an initial cracking of a quartz nucleus. What comes next is an accumulation of SiO2 on these nuclei in an over-saturated fluid. We can debate about the viscosity of the solution but that doesn't really change the basis of the theory in my opinion. I don't really think that the order/disorder boundary like described in many fluid-dynamics papers is causing the formation of the thread, but then again, maybe it is ;-) much study to be done still...
BTW I have recently collected some pretty wild faden quartzes. Have you ever seen a triple faden?

[Pierre Joubert]

Here is another example of a faden specimen that I collected a few months ago. The pocket yielded mostly 2 sided plates and clusters. This specimen has a neat faden at an angle across the specimen. On the other side, exactly on the other side of the faden, is a crack where minute crystal growth activity resumed. This faden was obviously the result of cracking and healing. The amazing thing is that while the crack is not straight, the faden pretty much is.

[Peter Lemkin]

Wow! What and excellent and interesting thread! Bravo to all involved. New information like this makes me appreciate my collection so much more and sends me back with a few specimens to my microscope.....

[C_Van-Hove]

Hi, I could add some pics and information about faden quartz,

- First it is not just quartz that can contain fadens, but also other minerals like epidote, garnet, adular, fluorite, and even pyrite

To me the faden is not really well crystallized at the beginning, I have found calcite inside faden quartz that wasn't crystallized due to calcite that arrives before the next crystallization period, like the image below, I know it's a faden due to the fact that it has been found where we often find faden quartz.

[C_Van-Hove]

here you can see small clefts that show us how we can have curved faden quartz (everytime the gangues aren't parallel and move in different directions)

[C_Van-Hove]

it begins to curve like this

[C_Van-Hove]

IMPORTANT : It is not the middle part of the quartz that breaks but the two parts nearer the rocks,
(as we often find fadens ended with a pyramid, and this pyramid doesn't contain any faden)

Until the moment the rock doesn't move too fast and not to far,
if the rock moves to far, the faden is broken and never continues growing, but the crystallization continues. I have found many quartz crystals with fadens really short compared with crystal size.

[C_Van-Hove]

Broken faden is often the base of scepter and fenster quartz.

[C_Van-Hove]

[Ronnie Van Dommelen]

Just wanted to share a Faden from a different locality. These are orange/red due to iron staining.

[Ronnie Van Dommelen]

And another from Nova Scotia.