Manual of mineralogy

A mineral may be defined as any naturally occurring chemical element or compound formed as a product of inorganic processes. This eliminates all artificial products of the laboratory as well as all natural products formed by organic agencies. The above definition is brief; and, though it embraces most of the substances considered as minerals in this book, it should be considerably expanded to be all-inclusive.

Minerals are the materials of which most of the rocks of the earth's crust consist and are, therefore, among the common objects of daily observation. The great majority of rocks are not made up of single minerals, but are more or less heterogeneous aggregates of several different species. A few rocks, like limestone and quartzite, consist of but one mineral in a more or less pure state. In addition to occurring as essential and integral parts of rocks, minerals are found distributed through them in a scattered way, or in veins and cavities. <...>