You may display the compositions of common AFM minerals on this diagram by clicking the checkboxes next to the mineral name abbreviations on the right. For minerals with Fe/Mg compositional ranges, you may change the (MgO/(MgO+FeO)) limits using the sliders. Notice that some minerals (Grt, Cld, St) are shown to be more FeO-rich, whereas others (Crd, Chl) are shown to be more MgO-rich. This reflects observed compositions of these minerals in metamorphosed shales. Compare the locations of the plotted minerals with their chemical compositions on the previous page to make sure that you understand the compositional plotting that results from the projection from Ms, Qz, and H2O.
For more information about the Thompson AFM Diagram:
Available for display on the AFM diagram are bulk compositions from published chemical analyses of Dutchess County metamorphic rocks. Use the pulldown menu under the DataSet heading on the right to plot all the avaiable analyses, or subsets of the data based on metamorphic zone or formation name. Mouseover a data point to see the source displayed to the left of the diagram. Data points are color-coded according to the following scheme: Chl Zone: green, Bt zone: brown, Grt Zone: red, Cld Zone: black, Crd Zone: blue; St Zone: orange, Ky Zone: DeepSkyBlue, And Zone: LightCoral, Sil Zone: gold, Sil+Kfs Zone: white. Notice that the bulk compositions of the rocks do not vary with metamorphic zone, consitent with the idea that metamorphism is largely isochemical.
If you want to see the contents of a Library DataSet, for more information or to see the format, click on the "View DataSet contents" button.
