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PhotosQuartz-beta - Kauaeranga Valley, Thames-Coromandel, Waikato, North Island, New Zealand

10th Aug 2017 13:32 UTCRalph S Bottrill 🌟 Manager

Quartz

Kauaeranga Valley, Thames-Coromandel District, Waikato Region, New Zealand

I don't know that we should label such crystals as quartz-beta when it's really a quartz-alpha pseudomorph? Unless it was photographed at over 550 degrees! Though we have four photos so-listed here already; these may have formed as such but they mostly lack the classic bipyramidal form so I am not sure if they warrant a label for the precursor phase?

10th Aug 2017 13:55 UTCPavel Kartashov Manager

Due to transparency of this crystal it is indeed quartz-beta of most low-temperature origin. Megatons of such bipyramidal quartzes growing right now in laterites worldwide.

This isn't paramorphose of -beta after -alpha - it is -beta from its beginning.

I observed such clear quartz "diamonds" up to 7-8 mm size from laterites of Adola in Ethiopia. Some of them contained rounded inclusions of latherite clays inside. The same story is with crusts of weathering over kimberlites in Angola. Bipyramidal quartz crystals grows up here up to 2-3 cm sizes, but overfilled with inclusions of surrounding minerals - hematite, serpentine, phlogopite, ilmenite and even real diamonds! ;-)

Look also on this photo https://www.mindat.org/photo-278636.html - this isn't overgrowth of alpha-quartz over beta-quartz of course.

10th Aug 2017 14:03 UTCUwe Kolitsch Manager

Fixed. (I just fix such stuff and don't bother to send complaints.)

10th Aug 2017 14:09 UTCUwe Kolitsch Manager

Five other photos fixed (one was an override one!!).

10th Aug 2017 14:16 UTCRalph S Bottrill 🌟 Manager

Thanks Uwe, I thought I should confirm the protocol.

Pavel, I think there is a lot of confusion on the term quartz-beta, but strictly speaking it's quartz that crystallised over about 550 degrees, not just bipyramidal quartz.

10th Aug 2017 14:35 UTCAlfredo Petrov Manager

Minerals can grow at much lower temperatures than their theoretical lower limits - Boracite and Cristobalite being two that come to mind. I do not understand it, but it happens, and is in fact quite common. Beta-quartz is perhaps similar in that in certain environments it can grow at ambient temperatures? I don't know, but it wouldn't surprise me.

10th Aug 2017 15:25 UTCPavel Kartashov Manager

i saw hundreds of thermograms of quartz bearing samples with beta-alpha transition in range 470-520 C^o. But I newer saw thermogram of quartz at all without beta-alpha transition peak, i.e. initial alpha-quartz. Alpha-quartz isn't diamond to be metastable.

10th Aug 2017 15:58 UTCUwe Kolitsch Manager

"Beta-quartz is perhaps similar ...".

No - it can't be stabilised.

10th Aug 2017 16:23 UTCAlfredo Petrov Manager

Then why does Pavel write: "Due to transparency of this crystal it is indeed quartz-beta of most low-temperature origin. Megatons of such bipyramidal quartzes growing right now in laterites worldwide. This isn't paramorphose of -beta after -alpha - it is -beta from its beginning." ?

Or are we talking in the laterite case simply of bipyramidal, no prism faces, "beta-quartz habit" that isn't internally a beta-quartz structure?

10th Aug 2017 17:37 UTCPavel Kartashov Manager

Hi Alfredo,

here is some misunderstanding. You should to read:

"Due to transparency of this crystal it is indeed quartz-beta of most low-temperature origin.

Megatons of such bipyramidal quartzes growing right now in laterites worldwide.

This [on the photo] isn't paramorphose of -beta after -alpha - it is -beta from its beginning."

Alpha-quartz is high-temperature hexagfonal polymorph forming in liparites bipyramidal xls. Buring alpha-beta transitions they change their volume and become translucent due to defects and dislocations.

Such paramorphoses often contains melt inclusions, rutile, magnetite and other anhydrous species.

Beta-quartz is usual low-temperature trigonal polymorph which also able to crystallize in bypyramidal morphology, but under lowest temperatures (far below 100 C^o) - in limestones under Moscow, in laterites, in Mongolian agate cavities etc. They very often are highly transparent and lustrous "diamonds" of different sort (Marmarosh etc.).

Such "diamonds" often contains inclusions of goethite, oil, clays and other hydrated minerals.

10th Aug 2017 18:25 UTCReiner Mielke Expert

Seems to be some confusion here as to what the stability field of Alpha and Beta-quartz are. According to what I read, Pavel claims Beta-quartz is low temp. but Ralph and Alfredo say high temp. So which is it? According to this site http://www.minerals.net/Quartz_polymorphs.aspx Beta-quartz is high temp.

10th Aug 2017 18:33 UTCUwe Kolitsch Manager

The "alpha-quartz" of Pavel is beta-quartz on Mindat.

The established nomenclature is that beta-quartz is defined as the high-temperature modification.

https://en.wikipedia.org/wiki/Quartz_inversion

10th Aug 2017 18:39 UTCReiner Mielke Expert

Maybe it is a translation problem. That would not be the first time.

10th Aug 2017 18:59 UTCPavel Kartashov Manager

When I learned, we were teached, that alpha- is more high-temperature polimorph (at all, not only for quartz), and betta-, gamma- etc are more low-temperature ones. This isn't problem of translation, but problem of schools.

In mindat sence, this is alpha-quartz formed under most low temperatures in supergenic environment.

10th Aug 2017 19:18 UTCReiner Mielke Expert

Problem of terminalogy.

10th Aug 2017 22:36 UTCRalph S Bottrill 🌟 Manager

The Mindat terminology is consistent with most international literature but maybe we should note it's different in Russia, if you have a reference we can add Pavel?

10th Aug 2017 23:49 UTCPavel Kartashov Manager

Ralph,

I am think it is not so important in this case.

More important, that here is low-temperature quartz crystal with morphology typical for most low-temperature its varieties.

I am agree to name it alpha-quartz.

12th Aug 2017 00:30 UTCRalph S Bottrill 🌟 Manager

Agreed Pavel, but I may make a note anyway on the quartz pages that there can be some confusion on this issue.

12th Aug 2017 02:21 UTCPavel Kartashov Manager

There also should to be stated, that alpha-quartz forms paramorphoses after beta-quartz - not pseudomorphoses. Composition don't changed during the replacement.

12th Aug 2017 08:31 UTCRalph S Bottrill 🌟 Manager

Good point Pavel, done.

I found another couple "beta quartzes" that I changed, but am not sure what to make of this one - https://www.mindat.org/photo-317455.html : suggestions welcome?

12th Aug 2017 20:27 UTCUwe Kolitsch Manager

The alpha/beta nomenclature of some minerals/compounds is often treated differently by chemists and materials scientists.

13th Aug 2017 00:35 UTCPavel Kartashov Manager

Ralph Bottrill Wrote:

-------------------------------------------------------

> Good point Pavel, done.

>

> I found another couple "beta quartzes" that I

> changed, but am not sure what to make of this one

> - https://www.mindat.org/photo-317455.html :

> suggestions welcome?

Looks like trydimite for me. I unable even imagine, why it was labeled as beta-quartz.

13th Aug 2017 15:16 UTCUwe Kolitsch Manager

I had already sent a complaint in 2010 (no reply); since then it was user-only.

Now deleted.

The caption of the six-sided tabular, colour-zoned (colourless-white) xls was:

"Spray of quartz-beta microcrystals, FoV 0,8 mm, on silicatic matrix, found in mine-debris together with scorodite, claudetite and argentopyrite by Thorsten Häuser, Photo and microchemical analysis (HF-dissolution) by W. Stoll"

13th Aug 2017 20:41 UTCRonald J. Pellar Expert

Correct me if I am wrong, but my understanding is that beta-quartz is not metastable at Standard Temperature and Pressure (STP0. in which case the quartz/beta-quartz is similar to acanthite/argentite with specimens of "beta-quartz" actually being pseudomorphs of quartz after beta-quartz. pointed out above by Ralph.

14th Aug 2017 02:31 UTCRalph S Bottrill 🌟 Manager

Thanks Uwe and Pavel, it was intriguing though, and I had wondered about Tridymite but the paragenesis was too weird. Maybe mimetite?

That's correct Ronald, though Paramorph is a more specific term, indicating a pseudomorph with no chemical change.

14th Aug 2017 02:36 UTCPavel Kartashov Manager

May be even usual barite. It is difficult to judge by photo, especially if it isn't known what exactly was dissolved in HF.

14th Aug 2017 18:51 UTCRonald J. Pellar Expert

Ralph, I a bit confused. I thought that paramorph was a term used for the actual presence of the a higher temperature form in a metastable state at STP. TA beta-quartz specimen at STP is in reality a quartz with the outward appearance of beta-quartz. which would make it a pseudomorph of the paramorph. :-)

To make things more complicated, how do you tell the difference between a quartz pseudomorph after beta-quartz and a Cumberland hapit quartz with no prism faces?

14th Aug 2017 19:14 UTCAlfredo Petrov Manager

"...how do you tell the difference between a quartz pseudomorph after beta-quartz and a Cumberland hapit quartz with no prism faces?"

Pseudomorphs are usually (I won't say "always", as Nature seems to delight in exceptions) fairly opaque, because they are polycrystalline aggregates. Rarely would a single crystal of one phase transform into a single crystal of a different phase. So that will distinguish "beta-quartz" from a nice clear Cumberland-habit quartz. How you'd distinguish it from a dirty opaque low-quality Cumberland habit, I don't know.

14th Aug 2017 21:03 UTCAmir C. Akhavan Expert

The definition I know is that a paramorph is the pseudomorph of one polymorph after another polymorph.

A morphmorphmorph, so to say.

The alpha/beta quartz phase transition is displacive - crystals that undergo a phase transition will stay clear because the atoms will not switch places and no chemical bond has to be broken. All that happens is that the SiO₄ groups are twisted slightly.

You can see that in any thin section of a granite or even better quartz-crystal-bearing rhyolite: the crystals that once grew as beta quartz are now homogeneous and clear, basically "featureless" alpha quartz crystals. Their surface is often roughened and many are cracked, which is what makes them look translucent.

Before quartz crystals were industrially grown, people tried to get rid of Dauphiné twin domains in natural rock crystals by repeatedly heating them above 573°C. With little success: the lattice defects behind the twin domains were fairly stable, and twin domains would appear again upon cooling, at the same position and with little change in their geometry. And of course the crystals stayed clear (otherwise they could not be used as oscillator quartz).

The distinction between a Cumberland habit crystal and a beta quartz is done by checking the geological environment and paragenesis: Low- to medium temperature ore deposits in sedimentary rocks? Not beta quartz.

Association with abundant calcite and/or dolomite? Not beta quartz.

Embedded in evaporites, carbonate-bearing sedimentary rocks, marbles? Not beta quartz.

etc.

It is unfortunate that people associate beta quartz with stubby hexagonal bipyramids, as these crystals grew inside a magma. I am not aware of any occurrence of stubby bipyramidal beta quartz that grew freely in a cavity - these seem to be elongated and either prismatic or more commonly more or less tapered.

I have this "prejudice" that any "Cumberland habit" crystal with a shiny surface (which indicates free growth in a cavity) cannot be a beta quartz (paramorph, that is).

14th Aug 2017 23:26 UTCPavel Kartashov Manager

Thank you Amir!

You well formulated what I would to say already some days.

We may to expect appearance of beta-quartz crystals only in magmatic and metamorphic rocks formed over 573°C. It is quite simple to distinguish them from more low-temperature rocks/associations.

For example, raremetal granites of Khaldzan Buragtag massif were formed from so alkaline melt, that magmatic crystallization of elpidite was possible. Additional evidense of it crystallization under unusually low temperature is morphology of its "pea-quartzes" fenocrystals. They has morphology of usual low temperature alpha-quartz with prismatic belt of faces, not bipyramidal beta-quartz crystals as in rhiolites of normal alkalinity.

15th Aug 2017 19:55 UTCRonald J. Pellar Expert

IPavel, Amir, is there a particular crystallographic property that prevents beta-quartz from forming prism faces?

15th Aug 2017 21:32 UTCAmir C. Akhavan Expert

The hexagonal prism is a "valid" crystallographic form of beta quartz, so there is no crystallographic reason/property for it not to form.

And of course beta quartz does show prism faces, even crystals that grew in magma occasionally do.

Why prism are often so small or absent on crystals that grew in magma is hard to say, but it has probably nothing to do with low vs. high quartz: Flick and Weissenbach (1978) have reported "cube quartz" that obviously grew as low/alpha quartz in rhyolites, and these also had very small or no prism faces.

Authigenic quartz crystals (which grew during the diagenesis of sedimental rocks and are often found still embedded in them) are often, but not always, stubby.

15th Aug 2017 21:36 UTCUwe Kolitsch Manager

It has probably to do with the surface energy of the prism faces.

16th Aug 2017 18:51 UTCRonald J. Pellar Expert

The Cumberland habit has always amazed me. Quartz being in the trigonal system and having chirality would require some very special growth conditions to grow forms that are almost an exact replica of hexagonal forms particularly in the "r" and "z" rhombohedrons. It would be easier for me to believe that the "Cumberland" habit was beta-quartz that grew near the phase transition and the temperature dropped to allow low temperature minerals to form (or in reverse order) with the result that there is a mis-reading of the paragenesis for the Cumberland habi Oh Well! Nature sure has a sense of humor. :-) (I do miss those emoticons.)t.

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