Two features make natural resources different. The first is that such resources are found in nature. From an economic point of view only extraction is required for the generation of wealth. This implies that natural resources require no prior productive processes. When something does not requires productive process then there is no previous productive chain. This means that extractive activity can be developed without strong linkages to society in the rest of the country. Therefore, extractive activities based on natural resources can be conducted in a way isolated from productive activities performed in the country.
The second feature is that natural resources, because they cannot be produced, at some point run out. Thus, they are non-renewable.
Examples of natural resources that reflect these characteristics are oil; minerals like silver, copper, gold, iron; and marine resources that are non-renewable.