CHAPTER I.
FORM OF MINERALS.
The physical
properties of a mineral comprise all those properties belonging to it
as a body existing in space, and consisting of matter aggregated in a
peculiar way. The more important of these are,—its form as shown in
crystallization ; its structure as determining its mode of cleavage
and fracture; its hardness and tenacity; its weight or specific
gravity; and its relations to light, heat, electricity, and magnetism.
Crystalline and Amorphous.—Mineral
substances occur in two distinct modes of aggregation. Some consist of
minute particles simply collected together, with no regularity of
structure or constancy of External form, and are named amorphous. All
fluid minerals are in this condition, together with some solid bodies,
which appear to tave condensed either from a gelatinous condition like
opal, when they are named porodine, or from a state of igneoue fluidity like, obsidian and glass, when they are named hyaline- The other class have their ultimate atoms evidently arranged according to definite law, and are named crystallim., when the regularity of structure appears only in the internal «*is-
