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 Post subject: Trapiche Garnet
PostPosted: Sun Oct 23, 2011 4:16 pm 
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Hello I just wanted to share this rare trapiche variety, it's an almandine garnet with orientated rutile needle inclusions.
Never seen before.

Image

4,18 cts
11,3 x 8,2 x 4,5 mm

Origin:
Tha-Beik-Kyin Township, west of Mogok, Burma (Myanmar)


regards
Ziggi

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 Post subject: Re: Trapiche Garnet
PostPosted: Sun Oct 23, 2011 5:14 pm 
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Hi Ziggi.
Very cool piece.

How are you defining "trapiche" in respect to this garnet?
Is it simply the star like pattern or does it refer to an actual growth phenomenon due to different growth rates?

Does the oriented rutile you describe contribute to the effect?

I've only heard of trapiche in beryl, corundum, chiastolite and more recently, tourmaline.


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 Post subject: Re: Trapiche Garnet
PostPosted: Sun Oct 23, 2011 5:57 pm 
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Hi Ziggi,

A really beautiful and unique stone!

Assuming that the silk is rutile, it looks as if something displaced the rutile...

Any idea of what could have caused the displacement?...

I've become very familiar with the star garnets found in northern Idaho. Rutile silk tends to concentrate within the core of the crystal and when oriented and cut properly, light reflecting off the rutile displays a star... rarely, a 6 ray star.

This looks like a "negative" 6-rayed star and is really fascinating. Thanks for posting!

-Martin
chasingthestarsbook.blogspot.com


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 Post subject: Re: Trapiche Garnet
PostPosted: Sun Oct 23, 2011 6:04 pm 
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I like that


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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 6:16 am 
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Well this trapiche is definitely caused by rutile, as the photos show. It seems that the milky areas are partially dissolved rutile needles.
If trapiche is defined by growth structure and orientated imbedding of a mineral during the epitaxy, well I would call this a trapiche, cause it’s a orientated rutile inclusions, which got strangely also dissolved in a orientated way.
In any way it’s a unique specimen which I have never seen before, at least interesting to see and study.

Kind regards
Ziggi


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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 7:29 am 
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could it be that the stone has been heated, which partially dissolved the rutiles needles?

have you looked for any other evidences of heating?


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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 7:37 am 
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I very much doubt that, cause it would effect the whole rutile inclusions and not bring up distinctive 6-ray pattern.

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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 12:49 pm 
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I don't know if it technically qualifies as a trapiche, but it definitely qualifies as awesome.


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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 5:09 pm 
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Barbra Voltaire wrote:
....I've only heard of trapiche in beryl, corundum, chiastolite and more recently, tourmaline.

seems there is also very rare Trapiche Spinel but i have not heard of trapiche garnet!

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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 5:49 pm 
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Thanks for posting more photos Ziggi!

Looking closely at the second photo- I'm intrigued by the striations in the center of the crystal. They can be seen in the patches of rutile around the center and seem to outline a crystal shape. I wonder if we're looking at polysynthetic crystal twinning that prevented the growth of rutile at the core?

Could this twinning somehow have continued to interfere with the growth of rutile at the junctions of the crystal faces and contributed to the trapiche effect?

Something prevented the rutile from growing in this area...

The only other possibility that comes to mind is that there is another mineral or inclusion that had a greater affinity for growing along the crystal face junctions than rutile does.... that would make it a a true trapiche gemstone. But, as Barbara said, no one has ever seen or heard of the trapiche phenomena in garnet. You'd think it would have been noticed somewhere in the world by now?...

I'm just a layman and am curious as to what others think caused this...

Also, note the oriented "starbursts" in the upper left of the photo. I've never seen that before... It looks as if rutile has grown from some sort of small crystal "seed" inclusion into the familiar 6-rayed star pattern.

Also Ziggi- the milky areas you described are most likely very fine rutile needles and not partially dissolved. I've noticed in some of the finer Idaho star garnet material the same incredibly fine silk layer. The best star garnet rough looks like silky plum colored glass. There was a recent (circa 2005?) scientific paper that measured the thickness of the rutile in Idaho Star Garnet and it was measured in nanometers.

There's a lot of interesting stuff going on here! I hope more people will comment on it.

-Martin
chasingthestarsbook.blogpsot.com


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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 6:08 pm 
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Quote:
“Trapiche” is a Spanish word for a press for sugarcane, and because of the resemblance of unique crystals displaying “six-pointed radial crystal pattern” or “six-pointed crystal form” to its grinding wheel “Trapicho”, the word became a gem term for such crystals.

so according to the definition can it be Trapiche Garnet?

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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 6:40 pm 
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Nevertheless one of the most interesting xls that poped up in he last months.

Thanks for sharing that beauty and, by the way, welcome to the crowd.

You are definitely in the right place here.

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 Post subject: Re: Trapiche Garnet
PostPosted: Mon Oct 24, 2011 6:48 pm 
roshanravan wrote:
Quote:
“Trapiche” is a Spanish word for a press for sugarcane, and because of the resemblance of unique crystals displaying “six-pointed radial crystal pattern” or “six-pointed crystal form” to its grinding wheel “Trapicho”, the word became a gem term for such crystals.

so according to the definition can it be Trapiche Garnet?


I'm lost.... Where does that definition of 'Trapiche' come from?

My humble and partial understanding of 'Trapiche' is that material (usually dark) concentrates in definite lines that relate to the crystal system of the host material. Most commonly, 'Trapiche' occurs in a hexagonal crystal system on the A/B axes. There is a similar occurrence in some trigonal material (there being still debate about the relationship of the hexagonal and trigonal systems). But then there is Andalusite (var Chiastolite) which is orthorhrombic and shows a near 90 deg cross relative to the C axis.

However, I have not yet read - let alone seen - of such a formation in a cubic system. Anyone else?...

Also, 'Trapiche' is a phenomenon distinct from asterism, te formation of 2/4/6-rayed reflection patterns that result (mainly?) from the presence of parallel Rutile threads in the host material.


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 Post subject: Re: Trapiche Garnet
PostPosted: Tue Oct 25, 2011 2:19 pm 
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Kerensky-

That definition of trapiche gemstones originated in Columbia. Emerald miners were the first to come across crystals that resembled a 'trapiche' grinding press/wheel.

Before I came across Ziggi's website, i didn't know that rubies and sapphires could display the same effect as columbian emeralds. Before this picture, I don't think anyone ever considered the possibility that this could occur in garnet.

I don't think the trapiche effect is limited to any one crystal system?... as you mentioned, chiastolite exhibits the same oriented growth of inclusions along the interface of crystal planes.

To me the great mystery is whether this pattern is caused by a mineral inclusion (perhaps microscopic) that grew along the crystal plane interfaces before or instead of rutile or due to some quirk of crystallography (which I have very limited knowledge of).

Right now, my thought is that this garnet grew from a "seed crystal" (the clean central portion in the second of Ziggi's close-up photos). Possibly, as the garnet continued to regrow at a later date, there was a deposition of some kind of mineral along the crystal interface. The rutile came later and grew where it could, it grew around the seed crystal and the crystal interface.

What lends credence to the possibility that the rutile grew later are the little "starburst" growths of rutile seen in the left hand side of the same photo. They seem to have grown out from some sort inclusion.

In some of the trapiche emeralds from Columbia, this same growth pattern is clearly seen. A flawless beryl crystal is surrounded by a carbon or albite inclusion from which the trapiche "arms" radiate from in a later and continued growth of beryl.

If this is the case, then we are looking at the only trapiche garnet known to the world.

Or possibly, this is a previously unknown phenomena related to garnet's crystal structure and growth. Is it possible for poly-synthetic twinning to cause some kind of interference that prevents the growth of rutile along the crystal interfaces?

Maybe this is a phenomena more common to gem garnet than we've yet known. Maybe it hasn't been noticed before because of the fact that rutilated garnets (especially those with good clarity) are exceptionally rare. Without the growth of rutile around this phenomena, we wouldn't be able to properly "see" this occuring. Also, a stone capable of displaying this would have to be cut just right to expose the phenomena- with the cut being parallel to a crystal face.

Going back to Idaho Star Garnets, it was awhile before it was discovered that to display the effect of a four or six ray asterism- a lapidary had to fashion the stone parallel to the crystal face. So yes, Kerensky, this is something different from asterism, instead of rutile growing along the crystal planes and reflecting light back in the form of a star, we have a halo of rutile around the same star pattern... along with a mystery of why and how it happened...

Once again, this is only a layman's speculation based on a study of one photo. I hope other, more knowledgable people comment on this stone and my ideas...

-Martin
chasingthestarsbook.blogspot.com


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 Post subject: Re: Trapiche Garnet
PostPosted: Tue Oct 25, 2011 2:59 pm 
Empyrean Gems wrote:
....this is only a layman's speculation based on a study of one photo. I hope other, more knowledgable people comment on this stone and my ideas...


Many thanks. It's certainly food for thought.


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