Thin section petrography
For a description of the mineral content of a rock we apply thin section microscopy under crossed polarized light. Polarized light, when traveling through a crystal is split up into two waves of different velocity which are resolved by a second polarization process just before the polarized light passes through the object lense. The interference of these two waves gives characteristic colours which help to identify minerals. Additional information for mineral identification is provided by the fact that polarized light microscopy gives information about the crystal symmetry. Moreover, thin section microscopy under plane polarized light can be applied to verify the results of crossed polarized light microscopy.
Polarized light microscopy is in particular useful for medium to coarse grained rocks, such as sparitic limestone, sandstone and most igneous (in particular plutonic) and metamorphic rocks.
In the case of sedimentary rocks thin section microscopy helps in the characterisation and identification of depositional and diagenetic conditions as well as in the quantification of pore space and evaluation of pore connectivity: information, which is of particular importance when evaluating reservoir and source rocks.