This section is covered in Chapter 3 of Nesse.
Refractometry involves the determination of the refractive index of minerals, using the immersion method. This method relys on having immersion oils of known refractive index and comparing the unknown mineral to the oil.
If the indices of refraction on the oil and mineral are the same light passes through the oil-mineral boundary un-refracted and the mineral grains do not appear to stand out.
If noil <> nmineral then the light travelling though the oil-mineral boundary is refracted and the mineral grain appears to stand out.
|RELIEF - the degree to which a mineral grain or grains appear to stand out from the mounting material, whether it is an immersion oil, Canada balsam or another mineral.|
When examining minerals you can have:
A mineral may exhibit positive or negative relief:
It is useful to know whether the index of the mineral is higher or lower that the oil. This will be covered in the second lab section - Becke Line and Refractive Index Determination.