Matte is a term used in the field of pyrometallurgy

Pyrometallurgy

Pyrometallurgy is a branch of extractive metallurgy. It consists of the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable metals...

 given to the molten metal sulfide

Sulfide

A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...

 phases typically formed during smelting

Smelting

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

 of copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

, and other base metals. Typically, a matte is the phase in which the principal metal being extracted is recovered prior to a final reduction process (usually converting

Converting (metallurgy)

Converting is a term used to describe a number of metallurgical smelting processes. The most commercially important use of the term is in the treatment of molten metal sulfides to produce crude metal and slag, as in the case of copper and nickel converting. Another, now uncommon, use of the term...

) to produce a crude metal. Mattes may also be used to collect impurities from a metal phase, such as in the case of antimony

Antimony

Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...

 smelting. Molten mattes are insoluble in both slag

Slag

Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...

and metal phases. This insolubility, combined with differences in specific gravities between mattes, slags, and metals, allows for separation of the molten phases.