Blue sapphire, also known as Neelam gemstone, belongs to the mineral species corundum. It has a hexagonal crystal structure and a hardness of 9 on the Mohs scale, making it a highly durable and scratch-resistant gemstone. Its refrective index range in 1.759 -1.770 and spesific gravity rage in 3.98 to 4.00 The color of blue sapphire can range from light to dark blue, and it is typically transparent to translucent. Blue sapphire can also exhibit asterism, which is a star-like pattern of light reflecting off the surface of the gemstone.
