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Metals occur in nature in two forms: native/free state (Au, Ag, Pt — low reactivity metals) and combined state (most metals as oxides, sulphides, carbonates, halides, or silicates). The key distinction between minerals and ores is economic: a mineral is any naturally occurring compound of a metal, while an ore is a mineral from which the metal can be extracted profitably. All ores are minerals but not all minerals are ores.
Important ores to remember: haematite (Fe2O3), bauxite (Al2O3.2H2O), copper pyrites (CuFeS2), zinc blende (ZnS), galena (PbS), cassiterite (SnO2), cinnabar (HgS), argentite (Ag2S), rock salt (NaCl), fluorspar (CaF2), limestone (CaCO3). Gangue is the earthy impurity (silica, clay) in the ore. A flux is added to react with gangue to form fusible slag: basic flux (CaO) for acidic gangue (SiO2), and acidic flux (SiO2) for basic gangue (FeO). The slag-formation reaction is critical in smelting operations.