It is a peculiar characteristic of minerals, that while plants and
animals differ in various regions of the earth, mineral matter of the
same character may be discovered in any part of the world,--at the
Equator or towards the Poles; at the summit of the loftiest mountains,
and in works far beneath the level of the sea. The granite of Australia
does not necessarily differ from that of the British islands; and ores
of the same metals (the proper geological conditions prevailing) may
be found of the same general character in all regions. Climate and
geographical position have no influence on the composition of mineral
substances.
This uniformity may, in some measure, have induced philosophers to
seek its extension to the forms of crystallography. About 1760 (says
Mr. Buckle, in his _History of Civilization_), Romé de Lisle set the
first example of studying crystals, according to a scheme so large as
to include all the varieties of their primary forms, and to account
for their irregularities and the apparent caprice with which they
were arranged. In this investigation he was guided by the fundamental
assumption, that what is called an irregularity is in truth perfectly
regular, and that the operations of nature are invariable. Haüy applied
this great idea to the almost innumerable forms in which minerals
crystallise. He thus achieved a complete union between mineralogy and
geometry; and, bringing the laws of space to bear on the molecular
arrangements of matter, he was able to penetrate into the intimate
structure of crystals. By this means he proved that the secondary
forms of all crystals are derived from their primary forms by a
regular process of decrement; and that when a substance is passing
from a liquid to a solid state, its particles cohere, according to a
scheme which provides for every possible change, since it includes
even those subsequent layers which alter the ordinary type of the
crystal, by disturbing its natural symmetry. To ascertain that such
violations of symmetry are susceptible of mathematical calculation,
was to make a vast addition to our knowledge; and, by proving that
even the most uncouth and singular forms are the natural results of
their antecedents, Haüy laid the foundation of what may be called the
pathology of the inorganic world. However paradoxical such a notion may
appear, it is certain that symmetry is to crystals what health is to
animals; so that an irregularity of shape in the first corresponds with
an appearance of disease in the second.--See _Hist. Civilization_, vol.
i.