Figure 9. First-derivative curves for 1 wt% hematite in calcium carbonate (top) and 1 wt% goethite in calcium carbonate (bottom). Both the hematite and goethite are paint pigments manufactured by Pfizer Chemical; the calcium carbonate is a reagent-grade manufactured chemical. Comparison of the first-derivative curves from these manufactured samples to hematite- and goethite-rich rock samples suggests the pigments embody the salient features of natural materials. The analytical wavelength range for the Minolta Spectrophotometer is 400-700 nm and, for the Perkin-Elmer Lambda 6 spectrophotometer, 250-850 nm.