Geology Reference
In-Depth Information
Chapter Summary
Matter is composed of chemical elements, each of which
consists of atoms. Protons and neutrons are present in an
atom's nucleus, and electrons orbit around the nucleus in
electron shells.
The number of protons in an atom's nucleus determines
its atomic number. The atomic mass number is the num-
ber of protons plus neutrons in the nucleus.
Bonding results when atoms join with other atoms;
different elements bond to form a compound. With few
exceptions, minerals are compounds.
Ionic and covalent bonds are most common in minerals,
but metallic and van der Waals bonds are found in some.
Minerals are crystalline solids, which means that they
possess an ordered internal arrangement of atoms.
Mineral composition is indicated by a chemical formula,
such as SiO
2
for quartz.
Some minerals have a range of compositions because dif-
ferent elements substitute for one another if their atoms
are about the same size and have the same electrical charge.
More than 3500 minerals are known, and most of them
are silicates. The two types of silicates are ferromagnesian
and nonferromagnesian.
In addition to silicates, geologists recognize carbonates,
native elements, hydroxides, oxides, phosphates, halides,
sulfates, and sulfi des.
Structure and composition control the physical proper-
ties of minerals, such as luster, crystal form, hardness,
color, cleavage, fracture, and specifi c gravity.
Several processes account for the origin of minerals,
including cooling magma, weathering, evaporation of
seawater, metamorphism, and organisms using dissolved
substances in seawater to build their shells.
A few minerals, designated rock-forming minerals, are
common enough in rocks to be essential in their identi-
fi cation and classifi cation. Most rock-forming minerals
are silicates, but some carbonates are also common.
Many resources are concentrations of minerals or rocks
of economic importance. They are further characterized
as metallic resources, nonmetallic resources, and energy
resources.
Reserves are that part of the resource base that can be
extracted profitably. Distinguishing a resource from
a reserve depends on market price, labor costs, geo-
graphic location, and developments in science and
technology.
The United States must import many resources to main-
tain its industrial capacity. Canada is more self-reliant,
but it too must import some commodities.
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Important Terms
atom (p. 63)
atomic mass number (p. 63)
atomic number (p. 63)
bonding (p. 64)
carbonate mineral (p. 71)
cleavage (p. 74)
compound (p. 64)
covalent bond (p. 65)
crystal (p. 66)
crystalline solid (p. 66)
density (p. 75)
electron (p. 63)
electron shell (p. 63)
element (p. 63)
ferromagnesian silicate (p. 71)
hardness (p. 75)
ion (p. 65)
ionic bond (p. 65)
luster (p. 74)
mineral (p. 62)
neutron (p. 63)
nonferromagnesian silicate (p. 71)
nucleus (p. 63)
proton (p. 63)
reserve (p. 78)
resource (p. 77)
rock (p. 76)
rock-forming mineral (p. 76)
silica (p. 70)
silica tetrahedron (p. 70)
silicate (p. 70)
specifi c gravity (p. 75)
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