In 2002, a new gem mineral of commercial importance was discovered. In accordance with the need for all new mineral discoveries to be scientifically characterized (see Nickel and Grice, 1998), the gemological community anxiously awaited the results of tests to positively identify the new mineral (Hawthorne et al., 2003, Hawthorne et al., 2004 and Laurs et al., 2003). This period of analysis brought into play the question: Exactly what procedures are necessary for the positive characterization of a new mineral?

These principal steps of identification are illustrated in the following case study for identifying a new mineral of the beryl group - pezzottaite.

The identification of this new mineral provided two major challenges: first, the determination of the exact chemical composition, and secondly, the identification of its crystallographic structure (the geometrical arrangement of the atoms in three dimensions (see Box 1, Figs. P2 and P6). From special technique of analysis (Boxes 4 and 5A), the exact stoichiometric chemical formula, and the space group of this new mineral, have to be determined (Box 1). As soon as the mineral was characterized (Boxes 1, 2, 3, 4, 5 & 6), the differences between already existing minerals had also to be investigated (see Nickel and Grice, 1998 and Box 5B) and a decision had to be made regarding whether a new mineral had been found, and, if so, what would be its new name? (Hawthorne et al., 2003 and Box 6). In the case of pezzottaite, these analysis provided major challenges. As pezzottaite contains light elements - such as hydrogen, lithium, and beryllium, which cannot be directly analyzed by quantitative methods commonly used for mineral analysis such as electron microprobe (EMPA) orXRFanalysis - direct measurement by Laser Ablation Mass Spectroscopy was also used (see Box 4B and Fig. P16), as well as conventional methods used for chemical analysis (Box 4A). In addition to challenges in the analysis of chemical composition, determination of different atomic positions in the crystal structure was not trivial.

ANALYZING THE CRYSTAL STRUCTURE

The secrets of the nature of a new mineral are so small we cannot even identify them with the help of microscopic magnification. One way to explore this atomic world is with X-rays (Figs. P3 and P17).

X-rays have a very short wavelength (with dimensions similar to atoms), allowing them to penetrate and interact with atoms in a mineral structure. As atoms group together at very short distances, X-rays are diffracted when passing through a crystal and change their direction when they interact with them. Furthermore, diffracted X-rays interfere with each other, just like water waves emerging from two ships. The interaction between atoms and X-rays depends, among other factors, on the geometrical arrangement of the atoms and can be interpreted with X-ray diffraction diagrams, and computer calculations. A diffraction pattern of a single crystal consists of symmetrically arranged spots, where the spot separation determines the periodicity of the lattice (unit-cell dimensions) and the arrangement of the spots provides clues to the symmetry of the structure.

Finally, the unit-cell and the space group can be determined (Boxes 1 and 5A). This is a crystallographic code that identifies the crystallographic nature of a mineral.