This is some SIMS data for one of my cherts. You can think of SIMS as counting individual atoms, so it's good for stable isotopes or simple elemental ratios, as seen here. From the plot, silicon has a constant concentration independent of carbon concentration, but nitrogen is dependent on carbon concentration. I had to create three custom symbols in IDL to make this plot (guess which one is the built-in symbol!). I also had to specifically add the extra tick labels on the top and right sides. The dashed line and annotations were added in Illustrator. The main point of this figure is that nitrogen is associated with carbonaceous material within the chert.