The terms mineral and rock are often confused. They are frequently used
together and the materials they describe are closely related. In
general, a mineral is a naturally occurring chemical element or compound
formed by inorganic processes, whereas a rock is a mixture of particles
or grains of several minerals.
However, when we refer to mineral resources or industrial minerals, we
generally include materials that are technically rocks—such as
limestone, dolomite, shale—and also coal and oil that are in fact
organic substances. On the other hand, we include in the rock category
high purity sandstone that is composed almost entirely of one mineral
(quartz) and high purity limestone that is composed largely of the
mineral calcite.