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):
In cross-section (looking down the c-axis) it looks like a kite:
Now spot the error(s) if any (still looking down the c-axis) in the following image:
Please motivate.
Again for eternal glory.
Last edited by Doos on Fri Oct 05, 2007 2:08 pm, edited 1 time in total.
Joined: Sun Nov 19, 2006 5:51 pm Posts: 481 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.
Joined: Sun Nov 19, 2006 5:51 pm Posts: 481 Location: Las Cruces, NM
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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