1. Metals and their alloys, for example iron, copper, steel, aluminium, etc.
2. Non-metals, for example rubber, glass, plastic, etc.
The metals can be additional classify as:
(a) Ferrous metals, and (b) Non-ferrous metals.
Ferrous metals are those which contain the iron as their major constituent, for example cast iron, wrought iron and steel.
Non-ferrous metals are those which contain a metal other than iron as their major constituent, for example aluminium, copper, brass, tin, zinc, etc.