Unknown #6
Download and view the crystal structure data
- Right click on Unknown_6.amc ( 105bytes Dec30 04) to download the crystal structure to your computer. (This file was modified from an AMC file in the American Mineralogist Crystal Structure Database).
- Once the file has downloaded to your computer, click on it to automatically start XtalDraw and open the file for viewing. You should see something like this...
- Try to resist looking at the mineral chemical formula (Edit > Chemical Formula) as this will probably be too big of a hint right off the bat.
Determine the identity of the unknown
Using your knowledge of crystallography and systematic mineralogy, and manipulating the downloaded structure in XtalDraw, answer the following questions to deduce the identity of the unknown. Check your answers by clicking on the "show answer" tabs which appear with each question.
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Is this mineral a silicate or non-silicate? Can you narrow it down to a more specific group based on the composition?
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What crystal system does this mineral belong to?
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...so what mineral is this?
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Marcasite - FeS
2 
Marcasite
Image courtesy of Amethyst Galleries.
The structure is from Buerger M J (1937) American Mineralogist 16:361;
Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie 97:504
You should have realized from the composition that the mineral was a Fe-sulfide. Pyrite is ruled out because of its isometric (cubic) crystal system. That leaves the other polymorph of FeS
2, Marcasite, which is orthorhomic.
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