The graph displays a USDA-NRCS soil texture ternary
To create the ternary for USDA-NRCS Soil Texture Class. firstly you need to prepare data as in Book "USDA-NRCS Soil Texture Class", There are end points of polygon of each segment and seperated by an empty row.
To know how to plot this graph, please download the above project file (in the Zip file). There is a Note window to show the detail steps for plotting this graph..