Natural endowments which can be utilised to satisfy our needs, provided they are technologically accessible, economically feasible and culturally acceptable, are termed as resources. Materials available in the environment become a resource only when human beings utilise the available technology and institutions created by themselves to transform the substances into usable products which have utility and fulfill human wants. Hence, resources are a function of human activity. Resources may be classified into renewable and non-renewble resources on the basis of their exhaustibility.