Spectra from a study of the basic copper phosphate minerals: Cornetite, libethenite, and pseudomalachite

The molecular structures of the basic copper phosphate minerals pseudomalachite, libethenite, and cornetite were studied using a combination of infrared emission spectroscopy, infrared absorption, and Raman spectroscopy. Infrared emission spectra of these minerals were obtained over the temperature range 100 to 1000 °C.

The infrared spectra of the three minerals are different, in line with differences in crystal structure and composition. The absorption spectra are similar, particularly in the OH stretching region, but characteristic differences in the bending regions are observed. Differences are also observed in the phosphate stretching and bending regions. The IR emission of the basic copper phosphates studied shows that the minerals are completely dehydroxylated by 550 °C.

Figure 1 shows the infrared absorption spectrum of the hydroxyl-stretching region of (a) pseudomalachite, (b) libethenite, and (c) cornetite.   Figure 2 is the infrared emission spectra of the hydroxyl-stretching region of (a) pseudomalachite, (b) libethenite, and (c) cornetite from 100°C to 600° at 50°C intervals. Figure 3 shows the intensity of the hydroxyl stretching vibrations of (a) pseudomalachite, (b) libethenite, and (c) cornetite as a function of temperature. Figure 4 is band centers of the hydroxyl stretching vibrations of (a) pseudomalachite, (b) libethenite, and (c) cornetite as a function of temperature. Figure 5 is bandwidth of the hydroxyl stretching vibrations of (a) pseudomalachite, (b) libethenite, and (c) cornetite as a function of temperature. Figure 6 shows the infrared emission spectra of the 700 to 1700 cm−1 region of (a) pseudomalachite, (b) libethenite, and (c) cornetite from 100 to 600 °C at 50 °C intervals. Figure 7 is the Intensity of the hydroxyl bending vibrations of (a) pseudomalachite, (b) libethenite, and (c) cornetite as a function of temperature. Figure 8 is the peak width of the hydroxyl bending vibrations of (a) pseudomalachite, (b) libethenite, and (c) cornetite as a function of temperature.