J.B. Thompson AFM Diagram. This page will scale and plot geochemical data in mole percent units from pre-selected datasets or from a dataset that you upload in weight percent units. Plotting coordinates of J.B. Thompson (1957) are used for the muscovite projection (A=Al2O3-3*K2O) and the potassium feldspar projection (A=Al2O3-K2O). Use the Ms and Kfs buttons on the upper right to switch between those projections. If the dataset does not have both FeO and Fe2O3 data, you can convert all iron to FeO (choose "FET") or 90 mole % of all iron to FeO (choose "Fe+2 = 0.9") with the select buttons on the left.
To select a composition dataset to plot, choose a DataSetSource and DataSet from the pulldown lists on the right. You may easily upload your own data in weight percent units from a comma separated value file (.csv) if the first row of the file has the oxide labels, and subsequent rows have sample data. Mouse over the plotted data points to display the Sample ID and Name, if these are included in the DataSet .csv file.
For most Library datasets, the metamorphic zones of the sample points are colored 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.
You may display the compositions of common AFM minerals by clicking the checkboxes next to the mineral name abbreviations on the right. For minerals with Fe/Mg compositional ranges, you may change the Mg# limit using the sliders.
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.
Bulk compositions of metamorphosed shales that contain significant modal plagioclase, appear more aluminous on the Thompson projection than their observed AFM mineral assemblages. To to correct for this, projection from plagioclase (and ilmenite and apatite) can be added by selecting the checkbox labeled "Add Pl Proj." .
