Unknown #7
Download and view the crystal structure data
- Right click on Unknown_7.amc ( 2kB 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.
- To get a bigger view of the structure, click on View > Alter Structure Limits > 3; enter a=1.00, b=1.00, and c=1.2; and click on the minus ("-") key to shrink the resulting structure to a reasonable size within your computer screen.
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? If silicate, what type?
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This is a phyllosilicate (sheet silicate).
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Based on the arrangement of tetrahedral and octahedral layers in this mineral, is this a clay, mica, or something else?
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What element occupies the the T-O-T units in this mineral?
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Mg, so the mineral is trioctahedral.
...so what mineral is this?
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Chlorite - (Mg, Fe)
3(Si,Al)
4O
10(OH)
2 dot (Mg,Fe)
3(OH)
6
Chlorite
Image courtesy of Amethyst Galleries.
The structure is from Phillips et al. (1980) American Mineralogist 65:112-122
Chlorite is the only phyllosilicate with the T-O-T O T-O-T O layered arrangement.
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