A spectroscopic study of irradiation coloring of amazonite: structurally hydrous, Pb-bearing feldspar.

Irradiation-induced colour in amazonite can develop only in K-feldspar having both structurally bound H₂O and Pb impurities. Amazonite colour is controlled by either 1) an absorption minimum in the beta spectrum between three overlapping bands in the ultraviolet and a broad band at 625 to 643 nm, resulting in a blue colour, 2) a combination in beta of one UV band and a broad band at 720 nm, resulting in a green colour, or 3) both of the above superimposed, resulting in a blue-green colour. -J.A.Z.