Introduction
Turquoise, a hydrated phosphate of aluminum and copper with the ideal chemical formula CuAl6(PO4)4(OH)8·4H2O, has been used as a gemstone for thousands of years and is still used today to create modern or traditional jewelry. It is indeed a very ancient material used for the production of jewelry, which has been used extensively in ancient times in Egypt, Persia, China, Mesoamerica, North America, South America and Europe (Beale, 1973; De’an, 2002; Domínguez-Bella & Herrero, 2012; Lowry & Lowry, 2010; Mathien, 2001; Pogue, 1915; Qin et al., 2015; Ruppert, 1983; Ruppert, 1982). Today, it is also a fine stone still in use in artistic productions that maintain traditional styles (mainly from North America) or in contemporary creations.
There is a wealth of literature on the identification of the various simulants and treatments applied to this gem. Many simulants exist today but also in historical periods (Elwell, 1979; Lowry & Lowry, 2010). These include odontolith (Reiche ...