Nickel mattes are sulfide-based intermediates produced by smelting nickel-bearing ores or concentrates; they are classified under 750110. Nickel oxide sinters and other intermediate products — including calcines and partially reduced oxides — fall under 750120. The key distinction is the chemical form and the processing stage at which the material is exported.

Yes — the line between a concentrate and a matte can be contested. Ores and concentrates belong in the chapter on ores, slag, and ash, while mattes are classified here as metallurgical intermediates. The degree of processing and the resulting chemical composition are the determining factors; a binding ruling or laboratory analysis may be needed for borderline materials.