Morphology, Crystal Chemistry, and Properties of Amazonite

The morphology, the crystal habitus (the combination of crystallographic forms and the relative development of these forms), the types of twins, and perthites of amazonites are characterized. The chemical composition of amazonite changes within wide limits, but it displays a distinct compositional evolution. The chemical trends described for amazonite are also reflected by the associated rare-metal and REE minerals in granites and pegmatites. Amazonites are characterized by a high degree of Al/Si order in the structure. All parameters obtained from X-ray diffraction as well as optical microscopy show that most of the studied amazonites belong to the high-ordered microcline. Optical absorption and EPR studies show that the characteristic blue-green color of amazonite is caused mainly by the formation of Pb and Al electron–hole centers and by the structural centers of Fe that lead to the corresponding absorption bands.