Reflectance diffuse and specular spectroscopy

Light (or near-ir and uv radiation) that is incident on opaque minerals is partly absorbed and partly reflected by them. There are two kinds of reflection processes that occurring when light is reflected from a flat polished surface of the mineral (specular reflectance) and that occurring when the light is reflected from the mineral after it has been finely powdered (diffuse reflectance). The latter arises from radiation that has penetrated the crystals (as in an electronic absorption spectrum) and reappeared at the surface after multiple scatterings in this case there will also be a specular component to the reflectance from light that is reflected from the surfaces of the particles. The specular reflectance of a flat polished surface of an opaque mineral measured at normal incidence can be related to the n and k terms of the complex refractive index (N) in which  

The commercial spectrometers designed primarily for undertaking transmittance measurements in the near-ir-visible-near-uv range commonly have attachments that enable specular reflectance measurements to be made on polished blocks (see Wendlandt and Hecht, 1966 Hedel-man and Mitchell, 1968). Specular reflectance measurements of small 

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