The chemical formula of Sapphire is indicated by Al2O3 or Aluminum Oxide. Sapphire is actually the non-red variety of mineral Corundum. Sapphire belongs to the Oxides and Hydroxides mineral class. It is most commonly used for gemstone purposes. Sapphire has various colors except red. This is so because the red variety of corundum is called ruby. Sapphire is said to be the second hardest natural mineral known to mankind. It is also known in among the general public as being blue in color, but it can be nearly any color, even colorless. Sapphire exhibits fascinating microscope images when viewed with the aid of petrographic polarizing light microscopes for mineralogists.

 

            The index of refraction shown by Sapphire under petrographic polarizing microscope is usually 1.76 to 1.78. It also shows 0.009 birefringence. The hardness measure of the mineral when it is evaluated using the Mohs scale method is usually found 9. It has no cleavage found even when closely evaluated under polarizing microscopes used in optical mineralogy. However, there can be rhombic parting visible most especially when specimen sample is evaluated more closely using the petrographic polarizing microscope for mineralogists. Sapphire is known to crystallize in the trigonal system of crystal formation. It is also known to be strongly pleochroic when viewed with the aid of polarized microscope. In the field of optical mineralogy, this means that the specimen exhibits different colors when viewed at different angles using the polarizing microscopes.