The selection of five naturally occurring selenite minerals that contain two different transition metal ions, Cu²⁺ and Co²⁺could be distinguished by near infrared spectroscopy. Dependence of composition on spectral properties is a key to mineral identification and differentiation of the members of the selenite group. The nature of the band positions and splitting of band components in the electronic spectra of Cu²⁺ selenites in the region 12400–8000 cm^–1 are in conformity with octahedral geometry distortion. The two split components which are observed for the Co²⁺ band near 9000 cm^–1 in cobaltomenites are considered as the vibrational satellites of spin-allowed transition 4T1g(F) → 4T2g(F). Bands observed at 6950 cm^–1, 6810 cm^–1 and 6700 cm^–1 are the overtones of OH stretches of structural water in selenites and a strong absorption feature near 6700 cm^–1 is the result of hydrogen bonding between (SeO₃)^2– and H₂O. These bands are shifted in cobaltomenites. A sharp absorption band at 5170 cm^–1 is a common feature in all the spectra of selenite minerals and is the contribution by the combinations of the OH vibrations of water molecules, ν₃ and ν₁. A series of overlapping bands around 4500 and 4100 cm^–1 is the result of the combination of the vibrational modes of (SeO₃)^2– ion in the minerals.

Keywords: chalcomenite, clinochalcomenite, cobaltomenite, NIR spectroscopy, Cu and Co-selenite minerals