Chemistry Reference
In-Depth Information
1.2.
MINERALS AND MINERALOIDS
Minerals
are the most abundant type of solid matter on the crust of the earth;
they are homogeneous materials that have a definite composition and an
orderly internal structure. Minerals make up most of the bulk of rocks, the
comminuted particles of sediments, and the greater part of most soils. Over
3000 minerals have been identified, and new ones are discovered each year.
Only a few hundred, however, are common; most of the others, such as, for
example, the
precious stones
, are difficult to find (Ernst 1969). Table 3 lists
common minerals and mineraloids. Many schemes have been devised for
classifying the minerals. In the scheme presented in Table 4, minerals are
arranged in classes according to their increasing compositional chemical
complexity.
TEXTBOX
2
THE STRUCTURE OF MATTER: ATOMS AND MOLECULES
Atoms
All matter is made up of very small units called
atoms
, the small-
est material units having recognizable, characteristic properties, identical
to those of the bulk. Atoms, which are the building blocks of the universe,
can exist either alone or in combination with others. The
chemical ele-
ments
, for example, are forms of matter made up of identical atoms, each
atom of an element exhibiting the same characteristic properties. When
extremely strong forces are applied to matter, however, atoms may break
up into smaller parts; this shows that the atoms are not single physical
units, but composites having a complex inner structure of their own. Study-
ing the processes by which atoms break up made it possible, during the
early twentieth century, to understand the inner structure of atoms
(Asimov 2002; Pullman 2001).
Atoms are made up of varying numbers of extremely small particles,
generally referred to as
subatomic particles
, whose size is too small to see
or measure even under large magnification.
Protons
,
neutrons
, and
elec-
trons
are examples of atomic particles. The
protons
, which bear a positive
electric charge, and the
neutrons
, which are electrically neutral, are con-
centrated in the atomic
nucleus
, located in the center of the atom, as
shown in Figure 2. Since the protons have a positive electric charge, the
atomic nuclei also bear a positive electric charge.
Electrons
, which are much
smaller than the protons and neutrons, have a negative electric charge and
move rapidly in pairs around the atomic nucleus. All the atoms of any
one
element
have the same number of protons and electrons and are,
