Asterism on a Green Stone?

Gary,

No images of star garnet; I'll try to get some later today. Meanwhile you may find this link helpful if you plan to visit Emerald Creek: Star Garnets

I was able to get this (poor) image of my cat's-eye Spencer opal triplet before my camera's battery gave out. As the stone is rotated vertically the color in the "eye" goes through all the spectral colors. The little bright spots are air bubbles meaning it's time to grind off the quartz cap and cut a new one: the stone was cut in 1975 and the adhesive hasn't held up.

Re: cutting star garnets. Yes, finding and orienting the stars can be frustrating. The almandine is friable and requires special techniques in sanding and polishing to prevent spalling. If you get lucky and decide to cut some let me know and I'll help all I can.

Richard M.

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Hi,

Talkin' about asterisms, I was trading star sapphire for 4 years in Madagascar, mainly buying rough and making them cutted by skilled cutters. Even if I consider myself being somewhat skilled in this particular kind of stone, there's something I don't understand well about these. I noticed that, smaller is the stone, better is your chance to obtain sharp stars, even if both big and small rough stones seem to share same optical features before cutting...

here are some samples, from my own site:



Mogok, I know you're more skilled than me, maybe you could have some scientific explanations about this?

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On 3/19/2004 6:30:14 PM Mister Stone wrote:

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Hi,

I noticed that, smaller is the stone, better is your chance to obtain sharp stars, even if both big and small rough stones seem to share same optical features before cutting...



I've cut quite a bit of star corundum and have a couple of theories about why that problem could exist. First, do all the larger "problem" stones have whitish areas in the center as your avatar appears to? Second, do you have any images of the larger problem stones in side view that shows their profile? Those two things may provide some clues.

Richard M.
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On 3/19/2004 12:05:36 PM DiamondExpert wrote:

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Richard:

Thanks for the further info on the star garnets!

Do you happen to have any pics?

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Gary,

Nearly all of my best finished and rough star garnets were stolen. This is the best 6-ray I have left and there are better ones. This image was made in direct sunlight so there's some glare. All legs are strong and are oriented properly despite the illusory skewing in the image. The toughest thing about cutting the material is figuring out where the stars are...it's not easy like corundum where they're always perpendicular to the c-axis.

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Richard - thanks for the pic! It's very nice, and a much sharper star than I had expected.

So, I take it that I need to ask around the Emerald Creek area to find out how, or if it's possible, to search in a 6-legged star garnet-rich area.

Since I don't cut, I'll have to find out if my local cutter can find the stars in these puppies, should I be so lucky to pick some up...

Hi,

Not too many stones from Idaho have distinct stars in ambient light. There's a reason for the old saying in those parts that "a friend is the person who can see the star in your garnet." Actually it's not that bad; fine stones are found but the proportion of fine to average is very tiny, as always in gem deposits.

There's some science for finding the stars when cutting complete crystals. I can forward detailed information at an appropriate time. Briefly, a sphere cut from a 4-ray crystal with uniform silk will have 12 stars corresponding to the 12 dodecahedral faces. When spheres are made from 6-ray crystals they display 12 6-ray stars and 6 4-ray stars. It can get rather confusing, especially if only crystal fragments are found.

Richard M.

That's a nice stone for sure, I've never seen a garnet with such a star before... Do you know where it is from?

All the best,

Thanks Mogok. The stone's from Idaho, U.S.A., the only place other than India that produces significant amounts of star almandine. The location is discussed in several posts in this thread. It's now closed to commercial mining and is controlled by the government which allows hobby collecting only.

Richard M.

Ok, thats an interesting point...
Anyway I'm not that specialist on garnets!
Thanks for the post!

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On 2/24/2004 1:37:29 AM valeria101 wrote:

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Cats eye jade (nephrite) is not... No idea what causes the 'eye' - it surely is not due to inclusions, but the estructure of the material itself). The material occurs both in Canada and Russia, and is more rock shop curiosity than gem. I believe that the Russian material is still nephrite, not the jadeite of the Urals or Central Asia.----------------

A few words about cat's eye nephrite (a.k.a. cat's eye jade). These are properly termed cat's eye actinolite. The reason has to do with the definition of nephrite. Nephrite is an intermediate member of the actinolite-tremolite series in the amphibole group. Nephrite specifically refers to a member of that series with a "felted" or random fibrous structure. If it has parallel fibers, it ain't nephrite, and thus, by definition, not jade. Analysis of the misnamed jade cat's eyes has shown that they are usually actinolite, but tremolites are also known.

As Valeria stated, the eye in these stones is created not by multitudes of fibrous inclusions, but by the fibrous structure of the individial crystals that make up this aggregate. This produces a much weaker eye than in other cat's eye stones. To accentuate the eye, such stones are typically cabbed with a pointed cab which, in cross section, almost resembles a pointed mountain.

The classic source for actinolite cat's eye is Taiwan.

i have some pictures of some 6 ray star garnet carvings on my site if youd like too see. www.msnusers.com/vossistcarvings

Does anyone know if you can get an asterism on lapis lazuli?

Date: 1/14/2005 2:166 AM
Author: excent
Does anyone know if you can get an asterism on lapis lazuli?

lapis is entirely opaque so no light can shine thru it.as far as i know asterism in impossible in lapis.

Not that I''m an expert in any way but that was my thoughts.  I have been sold a ring with 3 stones with perfect asterism on all 3 and it was sold to me as Lapis - I have put it under magnification and could find none of the normal little gold and white bits that you usually find on lapis.  The reason I bought it was because I was sure I was right and the jewellery store had incorrect details.  None of my books mention asterism on lapis and I have searched the web to see if there were any pictures or comments about it - so far - none....

It is the same colour as lapis (I have a rough bit of lapis at home) but am scratching my head as to what it could be....  Any thoughts on what else it could be by the colour???

Lapis? don''t think so... Dark blue, translucent to opaque and showing star could be syntetic star sapphire of some sort. There are a few kinds of syntetic that look like anything from top natural star sapphire to dark, opaque material showing an unusually strong star. Something like vista-03-04  down this page.

"The last type of star corundum is the trapiche star. Here the star affect is not create by needles but by other inclusions. In trapiche stars the star is static and does not move."

Vincent,

Do you know wether a sapphire may have both : asterism and trapiche star ? That would require 6 well oriented cat eyes but...

What do you feel about this point ?

Merci d''avance.

I have nifty a black star in my bag of gems and wasn''t really interested in the thing until this thread.

Is it true that a black star can either be a sapphire or diopside?

Date: 7/13/2005 6:33:02 AM
Author: colorchange

''The last type of star corundum is the trapiche star. Here the star affect is not create by needles but by other inclusions. In trapiche stars the star is static and does not move.''


Vincent,


Do you know wether a sapphire may have both : asterism and trapiche star ? That would require 6 well oriented cat eyes but...


What do you feel about this point ?


Merci d''avance.

Hi colorchange,

Yes a star on a trapiche sapphire is possible. I bought one few years ago in Burm while I was buyer for www.gemwow.com. It was a blue grey Trapiche sapphire that was also displaying a star. I have not the stone anymore now as it was sold around one year ogo on gemwow.com
may be the photo is still there...
Not sure... but as I''m in Kenya now with no time and low internet speed i cannot confirm you this point... Sorry.

All the best

Thanks a lot Vincent,

Was the one you bought looking like the one on the photo below ? (10 Ct, 13 x 9.5 mm)








I can't resist to the pleasure of showing you one of my star sapphires (125 Ct, 40 x 30 mm, unfortunately too flat). Star is perfect, unfortunately, photo is poor (simply taken with the flash of a compact numeric). It is quite translucent and probably from Mogok.


Thanks again Vincent.

Hello,
Well that''s the same kind of stone: Correct! The star due to the needles that was moving on the surface of the cabochon was exactly in the middles of the trapiche star which branch are fixed. But I''ve seen also one stone that I did not bought at this time that has a "moving star" located just over the trapiche fixed star... too bad I did not bought and studied this specimen...

All the best!

The stone I saw was coming from the Mogok mining area in Burma.

Thanks a lot Vincent,

Indeed, mine is also thought to come from Mogok, but it is so curious that I had some slight doubts on it''s authenticity  .
Excuse me if I''m too curious, but... how big was the one you bought and how much did you pay it about ?

Best regards, encore merci, j''apprécie énormément que vous preniez le temps de répondre. Bon voyage, vous avez de la chance d''avoir un tel métier !!!!

Henri

Hello Henry,

Well I dont remember at all the price I paid for this stone but it was around 15 carats I think. Whatever it was not really an expensive stone at this time, but now these stones are slightly more costly as there is more interest currently in the "Burmese special gems"... I think that the guy tried to sell me first for around $200 but then as usual I negociated... LOL
Now the second stone that i did not bought had the star exactly superposed to the trapiche star... This one I remember well: the guy wanted $500 for the stone which was set on a ring. The ring was a "lucky ring" and the guy was a specialist of such "lucky stones": You know most of the Mogok people are very religious or supersticious and they appreciate a lot amulets and "lucky gems" like sapphires with a pagoda color zoning design,...
All the best,

Thanks a lot Vincent,

I can see I haven''t been cheated on price.
That''s sad you didn''t buy the other one, would you go again to Burma and see such a star sapphire, just mail me .

Best regards

Henri