These characters of opaque minerals can be only discussed in optical mineralogy if rightly evaluated in reflected light of polarizing microscope. Most minerals that remain perfectly opaque from hand sample to thin section are most likely to exhibit a metallic luster under petrographic polarizing microscope. These samples are also very minute in size just like the iron ores. It has been clearly noted in optical mineralogy that when a metallic mineral of rock specimens are distinctly seen with the unaided eye, it is the rarely necessary to make a section for their determination. This is so because in optical mineralogy, the distinction will be easily done with the use of any blowpipe methods.

 

            Other properties of minerals such as cleavage, form, color, and luster can be recognized in the same manner as of the microscopic mineral specimens. It is clearly cited in optical mineralogy that the evaluation of these properties are done with the use only of the reflected light of polarizing microscopes for geologists. If the mineralogist is using the mirror type microscope, it is important that the beam of light from the reflector-mirror must be cut off by holding the hand over the mirror or by moving the mirror.