Minerals aurichalcite,

ZnO were present after this calcination, see Figures 3a and 3b. The XRD pattern of CuO was not resolved because the CuO reflections overlapped with undecomposed aurichalcite. XRD patterns of the synthetic sample calcined in a similar manner clearly showed the presence of both CuO and ZnO and no evidence for the aurichalcite structure (1 ). The mineral sample was therefore recalcined at a higher temperature of 400°C, after which no traces of aurichalcite were observed, and both the CuO and ZnO reflections were identified as seen in Figure 3c. The higher temperature needed for the complete transformation of mineral aurichalcite to CuO and ZnO, as compared to the synthetic sample, is most likely a result of the larger size and thickness of the mineral platelets. 

Figure 3. X-Ray diffraction spectra of the natural aurichalcite mineral (a), mineral aurichalcite calcined at 350°C for 4 hours (b), and the sample in (b) recalcined at 400 C for 4 hours (c).

Figure 4. Electron micrographs of mineral aurichalcite calcined at 400 C for 4 hours, (a) Bright field image, (b) Selected area diffraction pattern showing ZnO orientations with zone axes of [1010], [3031] and [5051]. See text for other ZnO orientations.

Figure 5b. Mineral aurichalcite calcined at 350 C for 4 hours. Schematic diagram showing epitaxial registry and similarities of d-spacinqs for the most intense aurichalcite and ZnO diffraction spots, n = ZnO with [3031] zone axis, ZnO with [1010] zone axis, and Q " aurichalcite near [101] zone axis. A = aurichalcite.

Figure 6a and b. Electron micrographs of mineral aurichalcite calcined at 350°C for 4 hours and reduced in a 1% H2/N2 gas mixture, (a) and (b) bright field images. 

Overall platelet dimensions of mineral aurichalcite did not appear to change during calcination, but became polycrystalline and porous. By dark field Imaging in the TEM, the ZnO particles were observed to be uniformly and highly dispersed. The porosity can be accounted for by the approximately threefold increase in density of Zn atoms upon decomposition of aurichalcite to ZnO. For this density change to occur with a constant overall platelet volume, pores must form. 

All diffraction spots in the aurichalcite mineral calcined at 400°C (Figure 4b) could be attributed to ZnO, except for four weak spots with a d-spacing of 0.192 nm. These spots matched well the Cu0 ll2 reflections with a reported value of d = 0.195 nm (6). Crystalline CuO was found to be present at this stage by XRD, as seen from Figure 3c. 

Aurichalcite mineral calcined at 350°C was analyzed in greater detail because it contained both aurichalcite and ZnO phases, and thus represented an intermediate state in the calcination process. 

Combined analyses by XRD and TEM showed that the aurichalcite mineral was sufficiently similar to the synthetic aurichalcite to be used as a model compound, to study the microstructural changes occurring during the catalyst preparation procedures. Calcination of the mineral and synthetic samples led to highly preferred orientations of ZnO. ZnO electron diffraction patterns with [lOlO] and [3031] zone... 

Because malachite and aurichalcite are carbonates, they will fizz when a bit of nitric or hydrochloric acid is added, due to the formation of carbonic acid and the snbseqnent evolution of CO2. Atacamite can be identified by treating a soln-tion of the mineral in nitric acid with silver nitrate. The chloride ion will react with the silver ion to form insolnble silver chloride (Table 8, solubility rule 3). 

Formula Chemical class Chemical type (Zn,Cu)5(C03)2(0H) Anhydrous carbonate with hydroxyl or halogen (AB)s(XO,)iZ, Crystal system Mineral group Space group Orthorhombic Aurichalcite B22,2... 

Chemical class Anhydrous carbonate with hydroxyl or halogen Mineral group Aurichalcite... 

Rosasite, aurichalcite, and associated minerals from Heights of Abraham, Matlock Bath, Derbyshire, 739 ... 

Aurichalcite is a copper-zinc carbonate hydroxide mineral with chemical formula (Cu,Zn)5(C03)2(0H)6. ft forms as a secondary mineral in the oxidising zone around copper and zinc deposits (such as Sahda, Colorado Lucin, Utah). The colour of aurichalcite varies from pale green to bright blue or green-blue and it forms as druse crystals in rock cavities, as encrustations, or as aci-cular crystals upon a matrix (Harding et al., 1994 Scott, 2002). 

Aurichalcite is closely related to the other blue or green zinc-copper carbonate minerals claraite and rosasite qq.v.), the latter of which has been identified as a pigment by Dunkerton and Roy (1996). 

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