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 Post subject: spot the error II
PostPosted: Fri Oct 05, 2007 1:57 pm 
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Hi,

During the last gem-a exam a topaz crystal was handed out and needed to be identified by looks alone.
A sample of such a crystal (taken from the internet):

Image

In cross-section (looking down the c-axis) it looks like a kite:

Image

Now spot the error(s) if any (still looking down the c-axis) in the following image:

Image

Please motivate.
Again for eternal glory.


Last edited by Doos on Fri Oct 05, 2007 2:08 pm, edited 1 time in total.

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PostPosted: Fri Oct 05, 2007 2:07 pm 
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Location: Las Cruces, NM
Topaz forms in the orthorhombic crystal system, usually dipyramidal class if I remember correctly (2/m 2/m 2/m). Therefore all 3 axes should be at 90 degrees to each other rather than at whatever they are in the illustration.

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Kevin
Handmade Enterprises LLC


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PostPosted: Fri Oct 05, 2007 2:09 pm 
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Hi Kevin,

Very good (and fast)!
There is another error aswell.


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PostPosted: Fri Oct 05, 2007 2:21 pm 
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I didn't think the obvious lenght of the lines was at issue. If lines a and b are taken to be relative lenghts, then they should not be equal. Orthorhombic crystals have their 3 axes of unequal lengths and at 90 degrees to each other.

At last I get to use that expensive degree for something.... :)

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Kevin
Handmade Enterprises LLC


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PostPosted: Fri Oct 05, 2007 2:27 pm 
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Hot dang! You're good.

Here is the correct image:

Image

Eternal glory for Kevin.


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