Egyptian blue is chemically known as calcium copper silicate (CaCuSi4O10 or CaO·CuO·4SiO2). It is a pigment used by Egyptians for thousands of years. It is considered to be the first synthetic pigment. The pigment was known to the Romans by the name caeruleum. Egyptian blue is a synthetic blue pigment made up of a mixture of silica, lime, copper, and alkali. Its colour is due to a calcium-copper tetrasilicate CaCuSi4O10 of exactly the same composition as the naturally occurring mineral cuprorivaite.