CLASSIFICATION OF MINERALS.. 131
tends much to render mineralogy more complex and difficult, and to destroy its scientific character.
In
collecting the species into higher groups, and arranging them in a
system, several methods have been pursued. Some, like Mohs, have
looke.d only at the external characters, and asserted that they alone
were sufficient for all the purposes of arranging and classifying
minerals. Others, led by Berzelius, have, on the contrary, taken
chemistry as the foundation of mineralogy, and classed the species by
their composition, without reference to form or physical characters.
Neither
system can be exclusively adopted, and a nat-ural classification of
minerals should take into account all their characters, and that in
proportion to their relative importance. Among these the chemical
composition undoubtedly holds a high rank, as being that on which the
other properties will probably be ultimately found to depend. Next in
order is their crystalline form, especially as exhibited in cleavage;
and then their other characters of gravity, hardness, and tenacity. But
the properties of minerals are as yet far from showing that
subordination and co-relation which has been observed in the organic
world, where the external forms and structures have a direct reference
to the functions of the living being. Hence, even when all the
characters are taken into account, there is not that facility in
classifying the mineral that is presented by the other kingdoms of
nature. Many, or rather most, of the species stand so isolated that it
is scarcely possible to find any general principle on which to collect
them into large groups, especially such groups as, like the natural
families of plants and animals, present important features of general
resemblance, and admit of being described by common characteristics.
Certain groups of species are indeed united by such evident characters,
that they are
