Unknown #10
Download and view the crystal structure data
- Right click on Unknown_10.amc ( 129bytes 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.
Show question #1
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What crystal system does this mineral belong to?
Hexagonal
Is this mineral a silicate or non-silicate?
Non-silicate
What element is C bonded to in this mineral, and what is the coordination of C?
Each carbon is bonded to three oxygens, forming triangular CO3 groups.
What class of non-silicate minerals does this belong to?
Carbonate
What is the coordination of Ca in this mineral?
Octahedral
...so what mineral is this?
Calcite - CaCO3
Calcite
Image from the New York State Academy of Mineralogy
The structure is from Graf, DL (1961) Crystallographic tables for the rhombohedral carbonates. American Mineralogist 46:1283-1316
The only other polymorph of CaCO3 is aragonite, but it is orthorhombic.
CalciteImage from the New York State Academy of Mineralogy
The structure is from Graf, DL (1961) Crystallographic tables for the rhombohedral carbonates. American Mineralogist 46:1283-1316
The only other polymorph of CaCO3 is aragonite, but it is orthorhombic.
