(op'-ti-cal prop'-er-ties) A subset of the physical properties of a mineral that are a function of the interaction of light with mineral composition and atomic structure. These properties include color, luster, index of refraction, dispersion, pleochroism, play of color, luminescence, and fluorescence. For more information on this topic, see Science of Minerals.
It is the physical properties of a mineral or gem having to do with optics, like dispersion, absorption spectra, regfractive index, asterims, and dichroism.