calcite is considered to be particularly important for its link with climate evolution and water resources on Mars. Moreover, calcite is also found in the Earth's atmosphere
calcite is a uni-axial birefringent material, so it has one optic axis and, instead of one refractive index, it has a dielectric tensor specified by two principal dielectric functions, the ordinary (mo) and the extraordinary (me) refractive indices. At 647 nm no=1.655 and ne=1.485. The imaginary part is assumed to be zero (Gosh 1999)
Dabrowska DD, Muñoz O, Moreno F, Nousiainen, Zubko E, Marra AC. Experimental and simulated scattering matrices of small calcite particles at 647 nm. Journal of Quantitative Spectroscopy and radiative Transfer, vol. 124, pp. 62-78, 2013
Dabrowska DD, Muñoz O, Moreno F, Ramos JL, Martínez-Frías J, Gerhard W. Scattering matrices of Martian dust analogs 488 nm and 647 nm. Icarus, vol. 250, pp. 83-94, 2015