title: Add texture classes to soil classification triangle via ggplot2
body: <p>I have some experimental data and would like to plot on the soil classification triangle to identify the texture. I am using the triangle found here:</p>
  
  <p><a href="http://www.ggtern.com/2014/01/15/usda-textural-soil-classification/" rel="nofollow">http://www.ggtern.com/2014/01/15/usda-textural-soil-classification/</a></p>
  
  <p>I want to display clay, sand and silt as points.</p>
  
  <p>Here is my data:</p>
  
  <pre><code>structure(list(Clay = c(1.67, 1.29, 1.1, 1.57, 1.52, 1.72, 1.53, 
  1.47, 1.34, 0.84, 1.18, 1.03, 1.1, 1.08, 1.41, 1.17), Silt = c(59.21, 
  59.39, 54.4, 57.65, 58.42, 60.17, 64.98, 60.67, 57.84, 55.73, 
  56.7, 50.8, 53.68, 57.92, 59.97, 56.62), Sand = c(39.09, 39.33, 
  44.5, 40.79, 40.04, 38.08, 33.47, 37.89, 40.81, 43.44, 42.11, 
  48.17, 45.24, 41.01, 38.63, 42.21)), .Names = c("Clay", "Silt", 
  "Sand"), row.names = c(NA, -16L), class = "data.frame")
  </code></pre>
  
  <p>Thanks for your suggestions.
  AT.</p>