Miscellaneous orthosilicates and isostructural minerals

The polarized spectra of staurolite, Fe2Al9Si4023(0H), accomodating tetrahe-drally coordinated Fe2+ ions (point symmetry Cm mean Fe-0 = 200.8 pm) and consisting of absorption bands spanning the 5,000 to 7,000 cm-1 region (Bancroft and Bums, 1967a Dickson and Smith, 1976), are illustrated in fig. 4.6 and discussed in 4.4.3. These bands completely mask any contributions from Fe2+ ions that might be present in centrosymmetric octahedral sites in the staurolite structure. The A, and CFSE parameters of tetrahedral Fe2+ ions in staurolite are estimated to be about 5,300 cm-1 and 3,700 cm-1, respectively. The spectra of the cobaltian staurolite, lusakite, illustrated in fig 4.7, indicates that tetrahedrally coordinated Co2+ ions have A, and CFSE values of about 6,500 cm-1 and 7,800 cm-1, respectively. 

Published spectra are available for various types of topazes, including Cr3+-bearing (Petrov et al., 1977) and irradiated (Aines and Rossman, 1986) sped- 

5 Crystal field spectra of transition metal ions 

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