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Geohavens: World of Rocks, Minerals, Gems and Gemmology :: Gemmology and Mineralogy :: Gemstone Identification
 So-called aquamarine
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| boblalux |
Posted on 21-04-2009 09:49
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Newbie Posts: 6 Joined: 21.04.09 |
I have just bought 2 small cut 'aquamarines', total 2.5cts, but I'm not happy! Their colour is magnificent - too good to be true, AND the ref.index is 1.775, the spec.gravity between 5-7 (too small for an accurate measurement). Any idea of what this could be? Thanks |
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| aloysiushan |
Posted on 21-04-2009 13:53
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Super Admin Posts: 41 Joined: 08.09.08 |
I'd need more information than that really. But I'd prefer to examine the stone before making conclusions. It might be blue zircon... or high index glass. Tough to hazard an opinion without pictures and other details. |
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| boblalux |
Posted on 22-04-2009 10:55
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Newbie Posts: 6 Joined: 21.04.09 |
aloysiushan wrote: I'd need more information than that really. But I'd prefer to examine the stone before making conclusions. It might be blue zircon... or high index glass. Tough to hazard an opinion without pictures and other details. Hello, Thanks a lot - I'd forgotten about zircon.I slapped it between crossed polarizers, and .... isotropic, therefore it must be a glass. I looked at it also at an angle, just in case the c-axis was at perpendicular to the table - still isotropic. The sw..., I got it from Ebay and he won't answer my mails. A clear case of having been had. By the way, 2 questions: 1. For want of anything better, when checking between crossed polarizers, I immerse the stone in water. Have you any common or garden household liquid which has a higher ref.index? Conc. sugar solution? 2. How can I find out the polarizing direction of each polarizer? I realise it's not important when solely checking for isotropism, but could come in useful when wanting to fing out the positions of the optical axes. Thanks Bob |
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| aloysiushan |
Posted on 22-04-2009 18:15
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Super Admin Posts: 41 Joined: 08.09.08 |
Have you checked under the loupe for gas bubbles or glassy swirls? Those are easy indications of glass. Regarding the checking of the direction of polarisation, one way is to view reflections off the water surface at an angle. Light reflected at a glancing angle to the surface of the water is plane polarised parallel to the surface of the water. If you rotated your polariods such that you no longer see reflection, you'd have found the perpendicular direction. Let me know if you have other fancy ways for determining that. Do you know other gemmologists or gem enthusiasts? Bring them all here! |
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| agianto |
Posted on 22-04-2009 18:56
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Junior Member Posts: 32 Joined: 10.02.09 |
Here is a good link for common liquids refractive index: http://www.robinwood.com/Catalog/Technical/Gen3DTuts/Gen3DPages/RefractionIndexList.html I have never used immersion for cross polarisation, does it really help? |
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| boblalux |
Posted on 23-04-2009 10:50
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Newbie Posts: 6 Joined: 21.04.09 |
Thanks, both of tou... Aloysiushan: can't find any gas bubbles or swirls; am awaiting a diffraction spectroscope, so that I can close in on the id - zircon, spinel etc. Also thanks for the tip - direction of polarisation. I'll see if I find any other interested gemmologists/enthusiasts. Agianto: thanks for the list/link, which I had already found. You may be right, it's not always necessary to immerse in definite cases, but in border-line isotropic/anisotropic cases it could be important. In future, I'll compromise and use a low-n liquid - water. Bob |
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| aloysiushan |
Posted on 24-04-2009 15:22
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Super Admin Posts: 41 Joined: 08.09.08 |
Some mineral oils can be used - I can't remember the name of the one my mentor used. |
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| junyi |
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| polaris1028 |
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| bushworlda |
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| bushworlda |
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