A number of approaches are used, all of which produce chemographic projections - projections of many components onto 2-dimensional diagrams.ДЄ typical metamorphic rock may have 8 or more important components. Most of the time, petrologists prefer to find some way to reduce the number of components to three so that triangular diagrams may be used. Sometimes petrologists create 3-dimensional diagrams to show a four component system, but such diagrams are frequently hard to visualize.ДЄFM diagram with some common pelitic minerals plotted. If a system has more than three components, it cannot be plotted in two dimensions. Systems With More Than Three Components & Chemographic Projections this particular reaction requires only two components, SiO 2 and Al 2O 3): Note also that Qz, Ky and Co plot on a line in this ternary diagram, so there is a (degenerate) reaction (i.e.

An = Gr + Ky + Qz, a terminal reaction.

Gr + Qz = An + Wo, a tie-line flip, and.

It is impossible, for example, for a reaction to occur such as Qz + Wo = Gr + An (which is neither a tie line flip or terminal reaction) because neither Qz nor Wo contain aluminum whereas both Gr and An are aluminous-to replace a non-aluminous mineral assemblage with an aluminous assemblage would violate the laws of conservation of mass!ДЇrom the diagram on the far left, we can identify the following reactions (there are more):

No other geometric arrangement of phasses (dots) can yield a reaction. Mass balance considerations allow us to predict the type of univariant reaction that is possible (right figure): either a 'tie line flip' such that A + B = C + D or a 'terminal' reaction where one phase (E) breaks down to three other phases (F, G, and H). Three-component systems can be plotted on triangular diagrams with the corners representing the components (left figure). Two kinds of reactions can be 'picked off' a triangular diagram: tie line flip reactions and terminal reactions, depending on the relative positions where the minerals plot.

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