The following statements summarize and describe many of the key terms and concepts presented in the chapter.
- A mineral is a naturally occurring inorganic solid possessing a
definite chemical structure that gives it a unique set of physical properties. Most rocks
are aggregates composed of two or more minerals.
- The building blocks of minerals are elements. An atom is
the smallest particle of matter that still retains the characteristics of an element. Each
atom has a nucleus containing protons and
neutrons. Orbiting the nucleus of an atom are electrons. The
number of protons in an atom's nucleus determines its atomic number and the
name of the element. Atoms bond together to form a compound by either gaining,
losing, or sharing electrons with another atom.
- Isotopes are variants of the same element but with a different
mass number (the total number of neutrons plus protons found in an atom's
nucleus). Some isotopes are unstable and disintegrate naturally through a process called
radioactive decay.
- The properties of minerals include crystal form, luster, color, streak,
hardness, cleavage, fracture, and specific gravity. In addition, a
number of special physical and chemical properties (taste, smell, elasticity,
malleability, feel, magnetism, double refraction, and chemical reaction to hydrochloric
acid) are useful in identifying certain minerals. Each mineral has a unique set of
properties that can be used for identification.
- The eight most abundant elements found in Earth's continental crust (oxygen,
silicon, aluminum, iron, calcium, sodium, potassium, and magnesium) also make up the
majority of minerals.
- The most common mineral group is the silicates. All silicate minerals have the
silicon-oxygen tetrahedron as their fundamental building block. In some
silicate minerals the tetrahedra are joined in chains; in others the tetrahedra are arranged
into sheets, or three-dimensional networks. Each silicate mineral has a structure and a
chemical composition that indicates the conditions under which it was formed.
- The nonsilicate mineral groups include the oxides (e.g.,
magnetite, mined for iron), sulfides (e.g., sphalerite, mined for zinc),
sulfates (e.g., gypsum, used in plaster and frequently found in sedimentary
rocks), native elements (e.g., graphite, a dry lubricant),
halides (e.g., halite, common salt and frequently found in sedimentary rocks),
and carbonates (e.g., calcite, used in portland cement and is a major
constituent in two well-known rocks: limestone and marble).
- The term ore is used to denote useful metallic minerals, like
hematite (mined for iron) and galena (mined for lead), that can be mined for a profit, as
well as some nonmetallic minerals, such as fluorite and sulfur, that contain useful
substances.
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