Diagnostic plot of the strength of the 9.7 μm silicate feature against the equivalent width of the 6.2 μm PAH feature suggested by Spoon et al. (2007). The CON-quest LIRGs and ULIRGs are plotted using data presented by Stierwalt et al. (2013); CONs are plotted as red triangles and non-CONs are plotted as white circles. The shaded and white rectangles indicate the approximate regions of the plot used by Spoon et al. (2007) to divide sources into different classes.