Minerals are the materials in which the metals or their compounds are found in the earth's crust. The amount of metal present is different in each mineral. All minerals cannot be used for the extraction of metals. Examples of minerals are haematite ( Fe 2 O 3 ) , cinnabar ( HgS ) etc.

Minerals are the materials in which the metals or their compounds are found in the earth's crust. The percentage of metal is different in each mineral. Some minerals contain questionable impurities which makes the extraction of metals more complicated, while others do not contain many impurities. Hence, all minerals are not used for extracting metals. An ore is a mineral from which a metal could be extracted profitably and conveniently. Ores have high amount of metal, and fewer impurities. For example, bauxite is an ore of aluminium.

In the process of metallurgy, the ores used are first crushed and powdered, and then concentrated by various methods. Following the concentration, the metal is now extracted from the ore. To achieve this, the ore is first converted into a compound which is easy to reduce. This is achieved by various methods including calcination. Calcination is a process of converting an ore into its metal oxide, by heating the ore in limited supply or absence of air, at a temperature which is just below its melting point. In this process, the moisture is removed, the volatile impurities get expelled, and the carbonate ores are converted into oxide ores since they are easy to reduce.