ABSTRACT
The elements are treated as resources in Chapter 22, although they are obtained as compounds in geological materials from which they are separated by processes involving heat and chemical treatments. The products have little resemblance to the starting materials. This applies most obviously to the metals. However, many rocks have uses that require only mechanical treatment, such as crushing or cutting, leaving them still identifiable as rock. The difference is relevant to resource use, exhaustion and recycling, as considered in Chapter 26, although recycling and primary resource conservation are equivalent only in special situations, such as the use of helium.
