Triangular Plots

A triangle plot which is also known as a ternary plot, is a graph of 3 variables. It is most often used in geologic studies to show the relative compositions of soils and rocks, but it can be more generally applied to any system of three variables. This diagram displays a triangular plot area in S.W. England on which soil textures defined as proportions of sand, silt and clay are plotted.

http://www.oga-lab.net/RGM_results/plotrix/soil.texture.uk/soil.texture.uk_001_big.png