gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology, Pre-Columbian jade; Costa Rica; Maya; exchange; iconography, lapidary, turquoise, amazonite, microcline, feldspar

Turquoise [Cu²⁺Al₆(PO₄)₄(OH)₈·4H₂O; triclinic system] is mineralogically an end member of the chalcosiderite–turquoise–ferric turquoise series. Archaeologically, it is one of the blue-green lapidary materials used by various Mesoamerican societies to produce a wide range of objects, including pendants, mosaic tesserae, and beads. However, Mesoamerican archaeological objects made of turquoise sometimes contain interspersed pieces of amazonite that appear similar to the naked eye but are chemically and mineralogically distinct. Amazonite [Pb(KAlSi₃O₈); triclinic system] belongs to the feldspar group and is a blue-green variety of microcline whose colour is caused by lead impurities located at strategic points within its crystal lattice. Recognition of the alternating use of these two minerals in archaeological artefacts raises two questions: Is everything archaeologically classified as turquoise actually turquoise, and what is the source of the amazonite raw material and its archaeological significance? The first question has begun to be answered through detailed re-examination of plaques and beads traditionally identified as turquoise by Mesoamerican researchers. Evidence has now been found for the alternating use of turquoise and amazonite at archaeological sites in the Northern, Central-Western, and Southern Mesoamerican cultural regions. One of the most significant examples is a mask from Malinaltepec, Guerrero, a serpentine mask partially covered by a mosaic of blue tesserae, more than 90% of which are amazonite, with the remainder being turquoise; red shell tesserae complete the design. The second question has been partially addressed through geological-mineralogical research and fieldwork. To date, one amazonite deposit has been identified in Mexico, approximately 60 km southeast of Valle de Allende, Chihuahua, where amazonite occurs in Cretaceous–Tertiary (?) pegmatites associated with the granitic rocks of the Sierra de Peñoles. Representative samples from this locality were selected for analysis by electron microscopy and inductively coupled plasma emission spectrometry (ICP). For comparison with archaeological material, four tabular amazonite pendants from the archaeological site of El Huistle, Jalisco, were also obtained for analysis using the same methods. Electron microscopy results have revealed only the principal feldspar components, and trace-element analyses are expected to provide more useful discriminating data. As for other amazonite deposits in Mexico, a very general reference (Schmiter, 1980) suggests the presence of the mineral in Oaxaca. Once more information becomes available regarding archaeological sites containing amazonite artefacts and the location and characteristics of additional amazonite deposits, it should be possible to determine the types of objects produced, the extent of their use and distribution, the periods during which they were utilised, and the probable trade and exchange routes through which amazonite circulated in Mesoamerica.