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Thread: Quiz time

  1. #21
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    Quote Originally Posted by Wallace View Post
    is it Alexandrite? I am not good with stones.
    I was going to go for alexandrite too.

    Dying to find out what it is now...

  2. #22
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    Could it be spinel? Or, hmm, maybe kyanite?

    (Just tossing out other blue stones I know of here!)
    Last edited by eirish; 24-04-2012 at 01:09 PM. Reason: guessing again!

  3. #23
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    Quote Originally Posted by ps_bond View Post
    Oh go on, it isn't every day you get to use the word pleochroism...

    When you mentioned the shadow on the pavillion, were you meaning that with a brilliant cut it should throw light from that surface as readily as the rest?
    Yes that's, exactly right, the brilliant cut is designated to exactly that, but its dependent on the refractive index of diamond. You could change the material to sapphire for example, but you would have to change the angles of the cut, this would then look like an odd shaped stone and make it harder to make standard settings.

    Strontium Titanate has been used for a diamond stimulant ( but not too often these days) it has the same (almost) refractive index to diamond , and is just about the only confusion possible ( it will fail a thermal diamond probe)

    This stone below ( a synthetic sapphire) has been cut like that, but just look at the depth !

    Click image for larger version. 

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  4. #24
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    While you are all deep in thought I'll put on mine which is much easier. This collection of chipped stones lives in the back of a drawer. It should be trashed, really, but I'm too mean. They represent failed rub down settings and to look at them is like a knife in my heart. As you will gather, small squares are the worst. Dennis.
    Attached Thumbnails Attached Thumbnails Box Of Shame.jpg  

  5. #25
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    Aww the box of shame: are they 3 beryl, tourmaline cab, dark citrine, amethyst and a rhodolite garnet, the bottom left one perhaps another tourmaline?

  6. #26
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    I thought the top cab might be labradorite? and the 3 squares peridot? I'd also vote for citrine, garnet, and amethyst but I think I'll guess fluorite for the other green square.

  7. #27
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    Quote Originally Posted by eirish View Post
    Could it be spinel? Or, hmm, maybe kyanite?

    (Just tossing out other blue stones I know of here!)


    Bingo

    There are two types of stone that can easily be mass produced, to just about any color buy adding additional elements (iron, titanium, chromium, copper magnesium, cobalt, vanadium etc. ) to the Verneuil process; Sapphire and Spinel (http://en.wikipedia.org/wiki/Verneuil_process) The strange color should make these two ring alarm bells.

    This stone is particularly nasty. The purple arrow points to what appears to be double refraction. This should eliminate all singularly refractive stone including diamond and CZ . Many double refractive stone the refraction is so slight you cant see it without polarization (I was lucky to capture it hear) AKA saphire. (http://en.wikipedia.org/wiki/Birefringence)

    It should also eliminate spinel, but Synthetic spinel is known for showing anomalous double refraction because of the growing process., which cause internal strain.

    The stone is in fact a synthetic cobalt spinel. Under a Chelsea filter the thing looks “radio active” (no pun intended)

    RI and SG confirm the diagnosis, but you cant do that from a photo

  8. #28
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    To run concurrently with the stones Dennis posted from his box of shame here is the one (well four) that I could not take a picture of yesterday due to no light.

    All the same material just 4 different cuts.


    Quiz stone group by kwant, on Flickr

  9. #29
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    Quote Originally Posted by Julian View Post
    This stone is particularly nasty. The purple arrow points to what appears to be double refraction. This should eliminate all singularly refractive stone including diamond and CZ . Many double refractive stone the refraction is so slight you cant see it without polarization (I was lucky to capture it hear) AKA saphire. (http://en.wikipedia.org/wiki/Birefringence)

    It should also eliminate spinel, but Synthetic spinel is known for showing anomalous double refraction because of the growing process., which cause internal strain.
    Wow, I'm chuffed that I guessed it correctly, but being a physicist I'm really fascinated by the explanation. I've done outreach activities with schoolchildren on strain-induced birefringence using two pieces of polaroid film, an overhead projector, and some bits of clear plastic. I bet you could use 3D glasses as well - must try that when I get home.

  10. #30
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    Quote Originally Posted by Julian View Post
    Bingo

    There are two types of stone that can easily be mass produced, to just about any color buy adding additional elements (iron, titanium, chromium, copper magnesium, cobalt, vanadium etc. ) to the Verneuil process; Sapphire and Spinel (http://en.wikipedia.org/wiki/Verneuil_process) The strange color should make these two ring alarm bells.

    This stone is particularly nasty.
    The purple arrow points to what appears to be double refraction. This should eliminate all singularly refractive stone including diamond and CZ . Many double refractive stone the refraction is so slight you cant see it without polarization (I was lucky to capture it hear) AKA saphire. (http://en.wikipedia.org/wiki/Birefringence)

    It should also eliminate spinel, but Synthetic spinel is known for showing anomalous double refraction because of the growing process., which cause internal strain.

    The stone is in fact a synthetic cobalt spinel. Under a Chelsea filter the thing looks “radio active” (no pun intended)

    RI and SG confirm the diagnosis, but you cant do that from a photo
    aaaah and I thought it was very pretty!

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