All corundum gemstones are knownas sapphires, with the only exception of the ruby-red variant which is called ruby. However, the name sapphire is very common for blue gemstones, but this blue should not be understood as the colour of clear sky, but all shades of blue up to very dark blue and even black.
Sapphire is found in a wide range of colours and shades.
Sapphire is a mineral that occurs asAl2O3single crystals. The colour is determined by impurities such asFe2+,Fe3+,Cr3+,Ti4+ orV4+.
It has a hardness of 9 on the Mohs scale, after diamond.
The rocks where sapphires have been found are called pegmatites, which through erosion processes have been transported and deposited in alluvium in river beds. The most important countries in sapphire production are Sri Lanka (formerly Ceylon), India, more recently the USA, Australia and Nigeria.