Move slider to see 3D animation

Figure 5.19. Al₂O₃-FeO-MgO-K₂O Composition Diagram. The chemical compositions of common minerals found in metamorphosed shales are plotted on a 4-component (FeO-Al₂O₃-MgO-K₂O) tetrahedral diagram to show geometrical features of projections from muscovite (Ms) or K-feldspar (Kfs) onto the Al2O3-FeO-MgO plane (AFM plane). Move the slider to rotate the diagram view, and to show projection lines (red) from muscovite. Most of the minerals, garnet (Grt), chlorite (Chl), chloritoid (Cld), cordierite (Crd), staurolite (St), and kyanite (Ky), have compositions in the AFM plane and are not affected by the projection. Biotite, K-feldspar, and muscovite do not lie on the AFM plane.

Chemical projections from 3-dimensions to 2-dimensions can be done graphically by drawing a line from the projection point (Ms) through the mineral (Bt) being projected and finding where that line intersects the projection plane (AFM). Imagine the projection point (Ms) as a light bulb and the projected mineral (Bt) being located where its shadow falls ('Bt') on the projection plane (AFM). Projection of Kfs from Ms occurs "negatively" because of the location of Kfs relative to Ms and the AFM plane.

If the metamorphosed shale reached equilibrium at T-P conditions above the breakdown of Ms, J.B. Thompson (1957) proposed using a Kfs projection onto the AFM plane. You can see a graphical version of that projection by clicking on the "Show Kfs Projection" button and using the slider.

You may use your mouse and scroll wheel to pan and zoom on any of the images. Click the "Recenter" button or move the slider to return to the standard view.

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