Integrating Research and Education > Crystallography > Cpx Geobarometer > Directions > Part 2: Examine the Structures of Natural Clinopyroxenes

Part 2: Examine the Structures of Natural Clinopyroxenes

Download the crystal structures

Based on the crystal structure visualization software you will be using, follow the step-by-step instructions shown in the tabs below for downloading the crystal structures of clinopyroxenes from alkalic, mafic to ultramafic rocks in Victoria, Australia.

  1. Go to the American Mineralogist Crystal Structure Database (more info) and enter the following data into the search interface. Be sure you select "Download cif" for the file format.


  2. Check all the structure files from the Dal Negro et al. (1989) study.
    • To download each file separately to your computer, click on each of the 15 hotlinked Clinopyroxene's one after the other.
    • To download all of the files together, check all the files you need, followed by Process Selected Data at the bottom of the page.
      Next, click on the hotlinked

      to download the data.
  1. Go to the American Mineralogist Crystal Structure Database (more info) and enter the following data into the search interface. Be sure you select "Download amc" for the file format.


  2. Check all the structure files from the Dal Negro et al. (1989) study.
    • To download each file separately to your computer, click on each of the 15 hotlinked Clinopyroxene's one after the other.
    • To download all of the files together, check all the files you need, followed by Process Selected Data at the bottom of the page.
      Next, click on the hotlinked

      to download the data.

View the crystal structures

Click on the downloaded file to view the structure in your visualization application.

You should see something like this...

You should see something like this...


Questions to answer

Open the file for sample FR-1 in your visualization program and answer the following questions.
  1. What is the crystal system for this clinopyroxene?
  2. Monoclinic
  3. What elements are housed within the pressure-sensitive M1 site, and what is the coordination number of this site?
  4. Al, Mg, Fe, Ti, and Cr are housed within the M1 site, which is octahedrally-coordinated.
  5. What is the volume of the unit cell (in Å3) for this natural clinopyroxene?
    Click on Edit > Structure to view the dimensions of the unit cell and the β angle. Calculate the volume of the unit cell with the formula V = abcsinβ.
    Click on Edit > Geometry File to find the volume of the unit cell.
    433.41 Å3
  6. Determine the unit cell volumes for the other samples you downloaded. How much does Vcell vary among these samples from the four volcanic localities in Victoria, Australia?

« Previous Page      Next Page »