Hence we see that granite consists of a mixture of three substances,
called quartz, felspar, and mica, the felspar being in greatest
quantity. Each of these substances possesses properties more or less
peculiar to itself, such as hardness, solubility in acids, specific
gravity, crystalline form, way of splitting, etc. Hence, each of these
substances has a _definite chemical composition and constant physical
properties_ which define them as _minerals_.
This definition may be understood to include such substances as coal and
chalk, which are the mineralized remains of plants and animals
respectively. Even water and gases of the atmosphere may be said to
belong to the mineral kingdom of nature, as plants and their parts are
said to belong to the vegetable kingdom, and animals and their parts to
the animal kingdom.