A few elements like carbon, sulphur, gold and noble gases, occur in free state while others are found in combined forms in the earth’s crust. Elements vary in abundance. Among metals, aluminium is the most abundant. In fact, it is the third most abundant element in earth’s crust (8.3% approx. by weight). It is a major component of many igneous minerals including mica and clays. Many gemstones are impure forms of Al₂O₃. For example, gems ‘ruby’ and ‘sapphire’ have Cr and Co respectively as impurity. Iron is the second most abundant metal in the earth’s crust. It forms a variety of compounds and their various uses make it a very important element. It is one of the essential elements in biological systems as well.

For obtaining a particular metal, first we look for minerals which are naturally occurring chemical substances in the earth’s crust and are obtained through mining. Out of many minerals in which a metal may be found, only a few are viable to be used as source of that metal. Such minerals are known as ores.

What is the formula of magnetite?

FeS₂

Fe_2​O_{3​ i}s Hematite
FeS₂​ is Iron Pyrite
FeCO₃​ is Siderite
Fe₃​O₄​ is Magnetite.