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Rutile? inclusions in topaz
  
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Pete Richards
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PostPosted: Nov 29, 2011 10:27    Post subject: Rutile? inclusions in topaz  

Topaz crystals from Tepetate, San Luis Potosi, (and possibly from Villa Garcia, Zacatecas) Mexico often contain inclusions of what has long been interpreted as rutile. These include long hairs, often curved, and occasional rings (see e.g. Mindat photo: http://www.mindat.org/photo-15172.html ). The recent English version of the ExtraLapis book on topaz contains (pg. 89) the interesting assertion that these are not rutile at all, but "goethite alteration rings" and etched dislocation channels. This is based on micro-Raman spectroscopy.

This assertion seems suspect to me. I don't think etched dislocation channels would be randomly oriented, as the hairs appear to be. The meaning of "goethite alteration rings" is unclear (altered goethite rings? rings of some other material altered to goethite?), but if it refers to ring-shaped defects now filled with goethite, I'd like to know more about the formation of ring-shaped defects....

I can certainly believe that some (or even many) of these specimens no longer contain the original included mineral, rutile or otherwise, but I wonder if the authors may have jumped to an erroneous conclusion about their origin, on the basis of a few specimens.

Does anybody have any information to confirm the presence of rutile (or other mineral) hairs and rings in these topaz crystals - some of them if not all of them?

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PostPosted: Nov 29, 2011 11:13    Post subject: Re: Rutile? inclusions in topaz  

Pete,

If you want an untrustworthy (and not scientific) opinion, it doesn't looks to me like Rutile but like Goethite, but this is just my feeling. More than this and without analytic tests, sorry, I can't say.
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PostPosted: Nov 29, 2011 11:56    Post subject: Re: Rutile? inclusions in topaz  

Pete Richards wrote:
Does anybody have any information to confirm the presence of rutile (or other mineral) hairs and rings in these topaz crystals - some of them if not all of them?

Hi Pete,
By complete coincidence and while working on something else, I have the 2004 January issue of the Journal of Gemmology right in front of me - the cover story is Coiled 'rutile' whiskers in a quartz single crystal by Ichiro Sunagawa, Alan Jobbins and Emma Tinnyunt. Not topaz as you are interested in, but discussion of a similar formation problem. In this case the conclusion was that the coil whiskers formed before the quartz growth (and much detail accompanies this).

Re that photo in Topaz which also appears in John Koivula's Photoatlas vol 2 page 744; just glancing at it, I wondered why goethite (shape and Raman?); in the Photoatlas it suggests epigenetic alteration (from what?). It also says that that locality is known for its ring shaped inclusions such as these. There are also several pages devoted to the limonite stained etch channels, appearing with different morphologies and including the effects of heat treatment altering the limonite to hematite, turning them reddish brown.Gems & Gemology Fall 89 has an original paper describing this entitled Thermal Alteration of Inclusions in "Rutilated " Topaz, by Robert Kammerling and John Koivula, page 165. As for why the etch channels are a tangled mess, similar to the whiskers in the quartz - dislocations during formation? (the ring and the tangled mess being two separate questions I think).

I have a sample of "rutilated" topaz from Jaroslav Hyrsl as an example of these coated etch channels appearing to many as rutile, leading to the misnomer.

Best wishes,
Elise

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PostPosted: Nov 29, 2011 12:16    Post subject: Re: Rutile? inclusions in topaz  

Interesting comments, Elise. I agree that the rings and hairs may be different things, but Occam's razor is buzzing loudly! In other situations where I've seen rings, they are of acicular minerals like boulangerite, and most of the crystals are normal hairs, only a few of them coiled into rings.

Sounds like the ExtraLapis Topaz article skipped over some important details that are in the Photoatlas, though even there it sounds like there was a precursor mineral, no longer there.

I have several samples of these rings in topaz, and on some specimens there is what appears to be rutile hairs on the matrix and dense aggregations of something that appears coherent (not limonite after something) at the base of some crystals. Guess I'd better try to get a look at these with SEM/EDS. Raman would be another good possibility.

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PostPosted: Nov 30, 2011 02:52    Post subject: Re: Rutile? inclusions in topaz  

Tourmaline needles are also found as inclusions in topaz (photoatlas).
But I wouldn't expect it as rings.

Photoatlas also mentions columbite in topaz, couldn't that fit?
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PostPosted: Nov 30, 2011 05:44    Post subject: Re: Rutile? inclusions in topaz  

Pete:

Assume you remember the article "Mineral Rings & Cylinders" by Richard Bideaux that appeared in Mineralogical Record, vol. 1, no. 3. No analytical evidence is provided, but he did call the ring in topaz from Mexico rutile.

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PostPosted: Nov 30, 2011 17:16    Post subject: Re: Rutile? inclusions in topaz  

I found 2 rutile rings inside an apatite crystal in Bolivia about 15 years ago, and have wondered why it only forms rings inside other crystals, not freestanding outside in vugs... any crystallographic explanation? Same question for pyrite, goethite or goethite pseudos after pyrite... why only INside other crystals?
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PostPosted: Nov 30, 2011 19:34    Post subject: Re: Rutile? inclusions in topaz  

Alfredo:

I've always suspected it has something to do with preserving delicate structures from chemical weathering and physical destruction. I have, for example, delicate filiform right-angle pyrite crystals preserved in quartz and Baryte. Shiny and bright as anything. But where one of them intersects the surface, it's a square hole filled with limonite.

I believe I have one of the boulangerite rings from Madoc, Ontario, with an exposed ring, whereas most of them are included in calcite.

My own opinion is that all of these things (unlike fluid inclusions and their related minerals) formed before being enclosed in what now preserves them. Every time I hear a description of a quartz crystal speared by a tourmaline, I cringe!

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PostPosted: Nov 30, 2011 20:27    Post subject: Re: Rutile? inclusions in topaz  

Pete, I'm just hypothesising here in my crystallographic ignorance, but is it possible perhaps that rings are under stress, or physically unstable, and easily desintegrate out in the open, if not fortuitously included in a crystal?

Otherwise I could understand how a sulphide ring might disappear by chemical weathering, but I'd expect a rutile ring to be more resistant. Nevertheless I've never seen a rutile ring except as inclusions. Could it be they're fundamentally physically flawed from birth? (Apologies for the lack of correct terminology.)
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PostPosted: Dec 04, 2011 14:12    Post subject: Re: Rutile? inclusions in topaz  

John S. White wrote:
Pete:Assume you remember the article "Mineral Rings & Cylinders" by Richard Bideaux that appeared in Mineralogical Record, vol. 1, no. 3. No analytical evidence is provided, but he did call the ring in topaz from Mexico rutile.

That is a neat reference article John - the SEM images are almost whimsical and not what one would imagine could be found inside a mineral.

He does cover some of the possible causes and the questions these inclusions raise. Regarding the photo of "rutile" in topaz in that article; that was based on Dana 1892. How would they have known it was rutile at that time (short of physically extracting it from a specimen), and not the lined etch channels, as was found more recently? Of the one shown, it says the ring was enclosed in a cleavage fragment - was the assumption made that it was rutile based on Dana 1892?

I attached a quick photo of my specimen mentioned above, looking at it culet-up -- face-up it looks like a "rutilated" gem and is often sold that way. You can see the structures radiating from a single point- does this still conform with it being an etch channel? After reading the MinRec article I went through everything I have in my study collection looking for rings of any type - jamesonite, pyrite, rutile...not a one. Rats!

Again, not to distract from Pete's inquiry-- perhaps as we said, the tubes/fibers and rings are separate genesis problems, or maybe one gives clues to the other. I am looking forward to what he finds out and photos!
Elise
PS - the article mentions open helical forms and shows one boulangerite (?) inside flurorite. In addition to the JOG coiled whisker paper mentioned above, these are the first I've heard of a solid helix (see our thread about helical inclusions: http://www.mineral-forum.com/message-board/viewtopic.php?t=1337 )



topaz013a.jpg
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Faceted topaz with tube inclusions; Brazil, 14mm (table down).
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topaz013a.jpg



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PostPosted: Jan 24, 2013 00:16    Post subject: Re: Rutile? inclusions in topaz  

Hello,
I read on this forum by chance a subject that interests me.
It is the nature of inclusions in topaz: rutile or not?
I'm an old collector of minerals and meteorites and I’m a retired chemist.
You can find my work on http://www.agab.be (in French).
I wish to discuss about inclusions in the topaz of Tepetape, San Luis Potosi.
Fine_Lame.
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PostPosted: Jan 24, 2013 01:19    Post subject: Re: Rutile? inclusions in topaz  

The Halls Gap, Kentucky locality has free standing pyrite rings, spirals, right angle zig-zag and straight bars and other diverse forms inside the small quartz geodes that are found there. These shapes seem not to have been affected by the presence of any other mineral although I know not how or why they formed that way, not having any training in crystallography.
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PostPosted: Jan 24, 2013 08:22    Post subject: Re: Rutile? inclusions in topaz  

Hi to everybody!
I too saw the picture on Photoatlas. by seeing the picture appearing in this forum, I would say rutile as an inclusion mineral. True it is much more common in quartz than in topas, but the appearance might suggest me this mineral. I might be wrong by saying it is a tourmaline inclusion, which is much more likely to be found inside a topas (as well as in a beryl) than a rutile inclusion. However the possibilities are several, as mentioned above this forum.
Greetings from Italy by Riccardo.

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