Occurrence of Metals: - The earth’s crust is the main source of metals. Soluble salts of the metals are also found in sea water. Metals occur in nature in native or uncombined form as well as in combined form. The occurrence of metal in native or in combined state in the earth crust along with a number of rocky and other impurities depends upon the chemical nature of metals. Metals having less electropositive character have less affinity for oxygen, moisture and other chemical reagents occur in free or metallic or native state i.e. uncombined state e.g. as compounds. The occurrence of metals is thus divided as

1.   Native ores :-Free state occurrence of metals is called native ore, mainly noble metals e.g. silver, gold, platinum, mercury, copper etc. native ores are usually associated with rocky material, sand, clay etc. pure metal lumps are known as nuggets.

2.   Minerals:- combined state occurrence of metals is called mineral, mainly metals with higher electropositive nature occurs as mineral. A mineral has definite composition and may be a single compound or a complex mixture.

The minerals rich in metal as well as form which the metals are conveniently and economically extracted are known as ores. All the ores are minerals but all minerals are not ore e.g... Both bauxite (AL₂O₃.2H₂O) and clay (AL₂O₃. 2SiO₂O) are minerals of aluminium. However extraction of aluminium is usually made from bauxite ore and not from clay. Thus, bauxite is an ore (as well as mineral) of aluminium.

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