Answer. Matte is a mixture of cuprous sulphide along with un-reacted ferrous sulphide (Cu2S, FeS). It is a molten mixture that contains about 45% copper.
Ferrous sulphide is oxidized to ferrous oxide, which reacts with sand to form a fusible material iron silicate (FeSiOa) called slag. It is a lighter material.
FeO(s) + SiO2(8) ———> FeSiO3(s)
(i). Matte is further heated in bessemer converted to blister copper
(ii). Slag is an impurity that is removed away.