Ternary Plotting Summary

  • Ternary diagrams are used by petrologists to show relationships among three variables.
  • One variable plots at each of the three corners of the diagram.
  • The variables plotted are typically chemical components.
  • The units of the variables are typically mass, moles, or volume (mode).
  • The diagram gridlines are percentages of each variable relative to the sum of the variables.
  • Horizontal gridlines show the percentage of the component at the top.
  • Gridlines inclined to the right show the percentage of the component on the right.
  • Gridlines inclined to the left show the percentage of the component on the left.
  • Because only two percentages are needed to plot a data point, the third percentage can always be used to check that your plotting or reading is correct.


Various ternary plotting aids can be found on the .

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