The optical absorption spectrum of tetrahedrally bonded Fe (super 3+) in orthoclase

Optical absorption spectrum measurements and spectral details are presented together with transition assignments and other interpretations for a lemon-yellow gem-quality specimen of iron-rich orthoclase. Only three principal bands--26500, 24000, and 22600 cm (super -1) --are resolved in the spectrum and are tentatively assigned to the ⁶ A ₁⁴ A ₁⁴ E(G), ⁶ A ₁⁴ T ₂ (G) and ⁶ A ₁⁴ T ₁ (G) transitions, respectively. The resolution of these bands only is due to encroachment into the visible region of intense background absorption centered in the ultraviolet probably due to the O (super 2-) Fe (super 3+) charge-transfer process. The sharpness of the 26500 cm (super -1) band is consistent with assignment to transition of the first field-independent state. The yellow color is due to absorption of blue light in the 400 to 450 m mu region.