By performing gold chloride microcrystal tests on samples of cocaine with adulterants at 10, 20, and 50 percent concentrations, trends in the changes of the crystal morphology can be linked to specific adulterants and concentrations. For cocaine/caffeine mixtures, the trend is elongation of one axis, additional branching, and brown discoloration of the crystals. At 50:50 cocaine/caffeine mixtures, branched spherical crystals and long needles appear. The trends for cocaine/lidocaine mixtures include elongation of one axis with an X-shaped middle axis. The axes continue to grow and branching decreases until at 50 percent, spherical clusters of needles appear. These results indicate microcrystal analysis can be used as a novel method for presumptively identifying not only cocaine but also the identity and concentration of the adulterant. (Published Abstract)