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»  » Asterism on a Green Stone?
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| Pages: 1 of 2: [1] 2 > |
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Asterism on a Green Stone? |
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| P: 2/18/2004 11:51:53 AM | |
katbadness Cut Rock Total Posts: 459 Last Post: 8/25/2005 Member Since: 1/29/2004 |
Hi, I have a curious question. Is there such a thing as asterism on a green colored stone (emerald, tourmaline, garnet, etc.)? My understanding is that asterims is has nothing to do with the color as much as the internal structure of the mineral itself. I have heard of asterisms on corundums (star sapphire, star ruby, even star yellow sapphire). I have also heard that this phenomena is displayed on other types of stones (quarts is the one I have heard). But in all my research, I have yet to hear asterims being displayed on something like.. an emerald for instance. Further Net browsing also yields no result for other green stones. The reason behind my question is because I'd love to give my bf a star Any thoughts? |
| Posted: 2/18/2004 11:51:53 AM | |
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There are 53 replies to this message. There are 30 replies on this page. |
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| P: 2/18/2004 2:06:53 PM | |
DiamondExpert Ideal Rock Total Posts: 1,243 Last Post: 6/20/2009 Member Since: 1/16/2003 |
Asterism in emerald is apparently not unheard of, but I have never seen one or even a picture of one...chatoyancy (cat's eye) is, of course, not common but better known. You could consider a green sapphire with asterism, but most greens are pretty ugly in my opinion - I have never seen one of these either. Another, not altogether serious, path might be quartz with asterism stained green -  - ya, OK I agree, forget it |
| Posted: 2/18/2004 2:06:53 PM | |
| P: 2/18/2004 8:39:02 PM | |
valeria101 Ideal Rock Total Posts: 14,048 Last Post: 4/30/2006 Member Since: 8/29/2003 |
If you ask about yellow or green star sapphires, most will just assume you must be joking! In spite this, they are out there... only not that many. You would have a good chance to find one from an Australian source: these are sort of a local celebrity which has yet to cross borders allot. One such sources could be simplysapphires.com and their Australian connections. Sure Garry could know more of these... No idea where to find a better piece online (this is a 35cts cab), but they can come in smaller sizes and different shades, transparent stones included. Emerald cats eye can be great, but stars are hardly "true" stars: no idea whether there are any with more than a secondary, faint eye crossing the first. The stones look like cats eye emerald with some extra glow. If a cat's eye stone would do, such emeralds are a true royal treat though. Star quartz... maybe, but "green" in this stone means "yellowish olive" and the asterism is never apparent without directional lighting.  Ana "The greatest experts are only as good as the sum total of what they have seen." [Souren Melikian] |
| Posted: 2/18/2004 8:39:02 PM | |
| P: 2/20/2004 6:11:12 PM | |
Pyramid Ideal Rock Total Posts: 2,914 Last Post: 11/11/2009 Member Since: 11/10/2002 |
Not an asterism but thought I would attach this link. http://www.yourgemologist.com/emerald.html I believe these are collectors pieces and not for sale but there is shown the very unusual pair of star trapiche emeralds and also a trapiche emerald. I have seen on the internet others buying trapiche gemstones but do not know how expensive or rare they are. Maybe one of the experts here could say? I don't know if you would say a trapiche is a star but it is similar I think. Pictures of both are on the above link.
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| Posted: 2/20/2004 6:11:12 PM | |
| P: 2/20/2004 6:37:41 PM | |
Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Hello, Wow Ana! Wow wow wow... Thats a fine piece! The best I've seen so far may be. Very nice... Do you known were it is from? Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/20/2004 6:37:41 PM | |
| P: 2/20/2004 8:59:39 PM | |
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valeria101 Ideal Rock Total Posts: 14,048 Last Post: 4/30/2006 Member Since: 8/29/2003 |
---------------- Australia, but no idea of the precise location though... Ana "The greatest experts are only as good as the sum total of what they have seen." [Souren Melikian] |
| Posted: 2/20/2004 8:59:39 PM | |
| P: 2/23/2004 4:27:51 PM | |
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katbadness Cut Rock Total Posts: 459 Last Post: 8/25/2005 Member Since: 1/29/2004 |
Thank you for the feedback folks! I really appreciate it. I'll share 2 pictures that started this whole asterism on a green stone discussion between me and my bf. He saw this star ruby picture:  and also this picture: .And then he said... Hmmm... I wonder if there's a star emerald or jade out there. 
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| Posted: 2/23/2004 4:27:51 PM | |
| P: 2/23/2004 4:37:26 PM | |
mike04456 Ideal Rock Total Posts: 1,441 Last Post: 3/28/2004 Member Since: 11/20/2002 |
Aha! That explains it. That second stone is not a star (asterism) but a cat's eye (chatoyancy). They are basically the same thing, but have different names because of the appearance--the only difference is the number of rays. 1 = chatoyancy, 2+ = asterism.
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| Posted: 2/23/2004 4:37:26 PM | |
| P: 2/23/2004 8:02:30 PM | |
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Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Hello, Yep, Law Gem is right... Asterism begins when 2 lines cross each other. A green gemstone that ca show 4 rays asterism is green diopside from Mogok. But ususaly green diopside are found as nice cat's eye stones. Star diopside are usualy more brownish blackish. I've heard one or while about emeralds with star but was never able to see one. For jade there is not such effect. Jadeite as nephrite is an agglomerate of very small crystals. You dont have there the orientated needle inlcusions or tube that give chatoyancy or asterism. Star peridot is possible, I've got one specimen... It is quite a rare stone in Mogok but I've seen several. Anyway the star is quite weak. Its more a curiosity for gemologists. For tourmaline, tsavorite, demantoid, chrysoberyl I dont know about asterism. But chatoyancy is of course possible for chrysoberyl (an even alexandrite) and tourmaline. All the best, Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/23/2004 8:02:30 PM | |
| P: 2/23/2004 8:11:21 PM | |
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mike04456 Ideal Rock Total Posts: 1,441 Last Post: 3/28/2004 Member Since: 11/20/2002 |
I too have "heard" about star emeralds but have never seen one or even a photo of one. If one were to actually exist and be reasonably attractive (color-wise), I would expect it to be quite expensive as a collector's stone. I doubt it would ever reach the consumer market.
I have seen star garnets but not demantoids or tsavorites. As mogok says, I don't think star jade is possible because it is polycrystalline.
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| Posted: 2/23/2004 8:11:21 PM | |
| P: 2/23/2004 8:12:32 PM | |
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Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Hello, I get back the photo of my star peridot... It was on a native Burmese ring and displaying a 4 rays star ( weak but visible). For reference the stone was 84 carats. The star in peridot is usualy not visible in small stones... All the best,  Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/23/2004 8:12:32 PM | |
| P: 2/24/2004 1:37:29 AM | |
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valeria101 Ideal Rock Total Posts: 14,048 Last Post: 4/30/2006 Member Since: 8/29/2003 |
That's one nice emerald. Here's one user friendly source of them. If you stll wander about star emeralds, there is a good chance that these guys know more. Star peridot! This is a new one... 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.  Ana "The greatest experts are only as good as the sum total of what they have seen." [Souren Melikian] |
| Posted: 2/24/2004 1:37:29 AM | |
| P: 2/24/2004 12:02:50 PM | |
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mike04456 Ideal Rock Total Posts: 1,441 Last Post: 3/28/2004 Member Since: 11/20/2002 |
----------------Yet another demonstration that every time you think some gem material only occurs a certain way, someone will come up with a sample that blows up all those assumptions. 
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| Posted: 2/24/2004 12:02:50 PM | |
| P: 2/24/2004 1:03:36 PM | |
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katbadness Cut Rock Total Posts: 459 Last Post: 8/25/2005 Member Since: 1/29/2004 |
Star peridot! WOW! That's a nice one, too. And cat's eye nephrite!! That is also very different. Hmmm..... Thank you for the references and help guys. I agree with LawGem.. ---------------- Well, given the oddity of nature... I will patiently look for one, then. My bf did say that if one can't be found, he'll settle for a star ruby! HAH! "Settling" for a star ruby... I know his taste, he'll want one that is transparent like shown below, but with a much stronger star. Anyway, in the meantime, thought I'd share with you generous guys and gals another curiosity of nature that I found.
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| Posted: 2/24/2004 1:03:36 PM | |
| P: 2/24/2004 1:18:11 PM | |
MC Ideal Rock Total Posts: 8,831 Last Post: 11/22/2009 Member Since: 2/8/2003 |
---------------- Ah, that ruby ring is to die for!  Michelle
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| Posted: 2/24/2004 1:18:11 PM | |
| P: 2/24/2004 1:37:51 PM | |
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mike04456 Ideal Rock Total Posts: 1,441 Last Post: 3/28/2004 Member Since: 11/20/2002 |
---------------- Well, then how about this one: http://famousdiamonds.tripod.com/rosserreevesstarruby.jpg This is the Rosser Reeves star ruby, a 138.72 ct stone. Unfortunately, it's not for sale, being part of the National Gem Collection in the Smithsonian.
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| Posted: 2/24/2004 1:37:51 PM | |
| P: 2/24/2004 2:39:14 PM | |
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katbadness Cut Rock Total Posts: 459 Last Post: 8/25/2005 Member Since: 1/29/2004 |
---------------- That is one *HUGE* ruby... Wow... Quick!! Don't let the bf see that one!! Otherwise I'd be eating ramen for the rest of my life!  ---------------- Thank GOD it's not for sale... Phew! I'm saved from myself again, apparently.
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| Posted: 2/24/2004 2:39:14 PM | |
| P: 2/25/2004 7:48:24 AM | |
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valeria101 Ideal Rock Total Posts: 14,048 Last Post: 4/30/2006 Member Since: 8/29/2003 |
Star ruby: good luck... going down to the source to find any decent one not listed on the stock exchange yet!  That (or a simmilar) yellow star was once posted on cherrypicked.com is this it? A certain shop semed to have all kinds of star sapphire I could think of and then some: on the web it goes under the name of UkGems although their site in not terribly representative of the business... Ana "The greatest experts are only as good as the sum total of what they have seen." [Souren Melikian] |
| Posted: 2/25/2004 7:48:24 AM | |
| P: 2/25/2004 10:31:42 AM | |
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DiamondExpert Ideal Rock Total Posts: 1,243 Last Post: 6/20/2009 Member Since: 1/16/2003 |
...and don't forget star spinel...not too common, but not expensive... |
| Posted: 2/25/2004 10:31:42 AM | |
| P: 2/25/2004 10:55:07 AM | |
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Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Hello Gary, Red 6 rays star spinel? Are you kidding? The only star spinels I've heard about are mined in the Thabeikgyin area in the west of the Mogok valley in Burma and they are very dark brownish with a 4 rays star that is not really obvious to see. The stone you present looks like a synthethic stone... Did you check it or submit to a laboratory? If its not that expensive, please just tell me where I can find such thing... I would like to study it in the gemological laboratory I'm working in... All the best, Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/25/2004 10:55:07 AM | |
| P: 2/25/2004 11:16:12 AM | |
Nicrez Ideal Rock Total Posts: 3,230 Last Post: 10/21/2009 Member Since: 1/21/2004 |
What causes these stars? Is it the chemical composition, like the appearance of a certain element, or is it more atomical, like a physical structure of the atoms? Just curious if it's something that is uniform in all the stared stones, or if each stone has it's own case that causes it...?
"Sometimes it's OK to throw rocks at girls...as long as they sparkle! |
| Posted: 2/25/2004 11:16:12 AM | |
| P: 2/25/2004 12:05:40 PM | |
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Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Hello, The star in star ruby and sapphire is coming from the reflection of the light on rutile (titanium oxyde) needles. It is a mirror effect. This is the reason why the star looks to move. These needles were exsolved of the ruby or sapphire structure during its cooling process. As rutile ans corundum dont have the same structure, the miscibility is quite low. At high temperature rutile can be in solution but the solobility goes down rapidly as the temperature decrease. The rutile needle will crystalise as needles in specific areas within the corundum structure. These needles are all the time orientated with 60 degre angles to each other. This is the reason we found 6 ray star corundum. Other than rutile hematite can also create 6 rays star effect in corundum. But in this case there is 30 degre angle difference with the star create by rutile. This is the reason we can find very rare 12 rays star sapphire that have 6 rays due to rutile and 6 rays due to hematite. The star in this case see all the rays connecting to each other. An other possibility of star stone is twin star where 2 crystals grow together with a different axis and direction. If there are rutile needles then they will crystalise in each crystal. We will then see a stone that have 2 6 rays stars with different centers... 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. That the story for corundum. Now in other stones like garnet rutile crystalise in 2 direction to the star will not be 6 branch but 4... Many stones can show star effect: Ruby, sapphire, garnet, quartz, peridot, diopside,... Here are to illustrate better inclusion photographs I did in my laboratory in ruby and sapphire: The first one show the typical internal world of a Mogok unheated ruby with short rutile needles in nest like pattern, along with euhedral crystals (probably apatite) The second show rutile needles like we found usualy in Sri Lankan sapphires: Long rutile needles. But to be true this photo was taken in a Mogok Unheated Burmese Sapphire. The third and the fouth photo are detailled rutile needles in a Mogok ruby and sapphire. You can clearly see the typical triangular shape of the needles with re-entrant angles and their disposition at 60 degre to each other. All the best,  Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/25/2004 12:05:40 PM | |
| P: 2/25/2004 12:14:29 PM | |
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katbadness Cut Rock Total Posts: 459 Last Post: 8/25/2005 Member Since: 1/29/2004 |
Mogok beat me to it. Here's a simple description that I found. "In gemmology, an asterism is an optical phenomenon displayed by some rubies, sapphires, and other gems of an enhanced reflective area in the shape of a "star" on the surface of a cabochon cut from the stone. Asterism is caused by dense inclusions of tiny, parallel, slender fibers in the mineral which cause the light to reflect a billowy, star-like formation of concentrated light which moves around when the mineral is rotated. This is usually caused by small needles of rutile (titanium oxide) in the case of ruby and sapphire. The stars may exhibit four, six, or more rarely twelve rays. The rays are reflections from the rutile crystal. Rutile can also cause a "cat's eye" effect in gemstones. Some specimens may display much stronger asterism than others, and some specimens may have areas where the inclusions are not present, leaving holes or empty areas in the star."
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| Posted: 2/25/2004 12:14:29 PM | |
| P: 2/25/2004 12:30:09 PM | |
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valeria101 Ideal Rock Total Posts: 14,048 Last Post: 4/30/2006 Member Since: 8/29/2003 |
I didn't know there is virtually no star spinel in Burma ! The ones below are suposed to come from Ceylon and at $30 a piece I did get some under a microscope for fun. I never took pictures of my stones (I have no hardware for it) though. The pictures attached come from the net (Cresla.com)... Ana "The greatest experts are only as good as the sum total of what they have seen." [Souren Melikian] |
| Posted: 2/25/2004 12:30:09 PM | |
| P: 2/25/2004 7:45:48 PM | |
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Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Hello, Well that's a fact Ana: I dont know about star spinels in Burma except this kind of brownish unatractive stones from the Thabeikyin area (difficult to find because mining there is not really allowed and if I remember well the area is very controlled by the army that has some mining there...) For the rest to illustate better the explanation about stars here are some visual examples: Photos from first to last: A 12 rays star sapphire: All the 12 branches connect to the same center: 12 branches due to rutile needles, 6 branches due to hematite platelets. This one is from Mogok, Burma. A twin star ruby: You can see 2 6 rays star with 2 different centers due to the fact that the cabochon was cut in a twinned stone. This star ruby was mined in Luc Yen, Vietnam. The you have then a trapiche star ruby with a static star from Mong Shu, Shan State, Burma Finally you have a 2 trapiche sapphire with also here static stars. Both stones are from Mogok, Burma All the best, Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/25/2004 7:45:48 PM | |
| P: 2/25/2004 7:47:50 PM | |
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Vincent Pardieu Cut Rock Total Posts: 408 Last Post: 3/7/2008 Member Since: 1/21/2004 |
Ooops... Sorry I've forgotten the photo in my precedent post! Here are...  Vincent Pardieu, "travel addicted gemologist". |
| Posted: 2/25/2004 7:47:50 PM | |
| P: 3/18/2004 9:55:03 PM | |
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DiamondExpert Ideal Rock Total Posts: 1,243 Last Post: 6/20/2009 Member Since: 1/16/2003 |
I just learned that garnet (I think pyrope and almandine, but not sure) also can have asterism!...4 and, rarely, 6 ray stars! They are found only in Nothern Idaho, www.fs.fed.us/ipnf , and India...got this from the May issue of Rock & Gem. You can go hunt them yourself for about $10! ...learn something every day... 
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| Posted: 3/18/2004 9:55:03 PM | |
| P: 3/18/2004 11:06:01 PM | |
Richard M. Ideal Rock Total Posts: 929 Last Post: 11/22/2009 Member Since: 2/17/2004 |
---------------- I've dug and cut many of them, D.E. Learning how to find the star and cut them with the apex centered on top involves quite a learning curve!  Idaho produces the finest star almandines in the world. Four-ray material is pretty common but six-ray stones come from an area where the Forest Service generally won't allow digging. Good six-ray stones are hard to come by. Asterism also occurs now and then in the "rhodolite" pyrope-almandines from Africa and probably other garnet types that have properly-oriented rutile inclusions. There's a photo of a rhodolite star stone in "Garnet" by John D. Rouse. Richard M. |
| Posted: 3/18/2004 11:06:01 PM | |
| P: 3/18/2004 11:39:28 PM | |
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Richard M. Ideal Rock Total Posts: 929 Last Post: 11/22/2009 Member Since: 2/17/2004 |
Have any of you seen cat's-eye opalite from Africa? This one is not an especially good example because the eye isn't sharp but it's the best image I could find. The opalite apparently is a pseudomorph after replacing a fibrous material like asbestos. I've never seen a gemological analysis but it certainly cuts fine cat's-eyes in numerous colors. It cuts very nice stones that at their best look very much like chrysoberyl. I have a small amount of rough in grey, reddish and several shades of yellow to yellow-brown. Richard M.  |
| Posted: 3/18/2004 11:39:28 PM | |
| P: 3/19/2004 12:37:21 AM | |
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Richard M. Ideal Rock Total Posts: 929 Last Post: 11/22/2009 Member Since: 2/17/2004 |
Writing about Idaho and star stones as I did in a previous post, has anyone in the group seen precious opal stars and cat's-eyes? Idaho has both. An opal deposit near Spencer, ID yields some of the world's finest triplet-making opal. The opal was deposited inside nodules that formed in a perlite flow, no doubt geologically related to nearby Yellowstone National Park. The opal is useful mainly for triplet cutting because absolutely flat thin bands of incredibly bright precious opal are interlayered with white common opal. Now and then a phenomenon unique in the world occurs resulting in star and cat's-eye stones. Research done in 1975 at the CSIRO Division of Triobophysics, University of Melbourne, Parkville, Victoria, Australia stated that: "Their optical diffraction patterns have been found to contain strong intersecting 'rays' of color confirming that the gems are justifiably called 'star opals'...the packing arrangements which produce them are ...different from those found previously for Australian opals." These patterns yield single streaks of color at 60-degree intervals as the opal is rotated producing cat's-eye stones after being cut into triplets. Other diffraction patterns yield stars with both three and four legs as triplets. These stones are very rare and not well known. Richard M. |
| Posted: 3/19/2004 12:37:21 AM | |
| P: 3/19/2004 12:05:36 PM | |
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DiamondExpert Ideal Rock Total Posts: 1,243 Last Post: 6/20/2009 Member Since: 1/16/2003 |
Richard: Thanks for the further info on the star garnets! Do you happen to have any pics? My sister-in-law lives in Bonner's Ferry and the family has several cabins on Priest Lake, so I may make a trip up there this summer to do a little digging. I assume it takes someone experienced with this material to get a good looking cab. |
| Posted: 3/19/2004 12:05:36 PM | |
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