Minerals—The Building Blocks of Rocks - The Changing Earth: Exploring Geology and Evolution - page 61

INTRODUCTION
The term mineral brings to mind substances that we need
for good nutrition, such as iron, calcium, and magnesium;
however, these are actually chemical elements, not miner-
als, at least in the geological sense. Ice, on the other hand,
is a mineral because it meets all criteria in the defi nition of
a mineral—that is, it is an inorganic, naturally occurring,
crystalline solid , meaning that its atoms are arranged in a spe-
cifi c three-dimensional pattern, as opposed to glass, which
has no such orderly arrangement of atoms. In addition, ice
has a specifi c chemical composition (H 2 O) and characteris-
tic physical properties such as hardness, density, and color. In
sum, a mineral is an inorganic, naturally occurring, crystal-
line solid, with a narrowly defi ned chemical composition and
characteristic physical properties.
We cannot overstate the importance of minerals in
many human endeavors. Ores of iron, copper, manganese,
and chromium, as well as minerals and rocks for fertilizers
and animal feed supplements, are essential for our economic
well-being. Much of the ink used in the brilliantly colored
medieval manuscripts came from minerals, and the luster
of lipstick, glitter, eye shadow, and paints for appliances
and automobiles comes from the mineral muscovite. The
United States and Canada owe much of their economic suc-
cess to abundant minerals and energy resources (natural
resources), although both nations must also import some

essential commodities. Indeed, the distribution of natural
resources is one important consideration in foreign policy
decisions.
One important reason to study minerals is that they are
building blocks of rocks; so rocks, with few exceptions, are
combinations of one or more minerals. Granite, for instance,
is made up of specified percentages of minerals known as
quartz and feldspars along with other minerals in minor
quantities. In several of the following chapters, we will have
more to say about the importance of minerals in identifying
and classifying rocks.
Some minerals are attractive and eagerly sought by collec-
tors and for museum displays (

Figure 3.1). Other minerals
are known as gemstones —that is, precious or semi-precious
minerals or rocks used for decorative purposes, especially
jewelry. The precious gemstones, such as diamond (Figure 3.1a),
ruby, sapphire, and emerald, are most desirable and most
expensive. Amber and pearl are included among the semi-
precious gemstones, but are they really minerals? Amber is
hardened resin (sap) from coniferous trees and thus an or-
ganic substance and not a mineral; nevertheless, it is prized
as a decorative “stone” (Figure 3.1b). It is best known from
the Baltic Sea region of Europe where sun-worshiping cul-
tures, noting its golden translucence resembling the Sun's
rays, thought that it possessed mystical powers. Pearls form
when molluscs, such as clams or oysters, deposit successive

◗

◗ Figure 3.1 Precious and Semiprecious Gemstones

Even though amber is an organic substance, it is nevertheless
valued as a semiprecious gemstone.

b

Strands of variously-
colored pearls at the
world-famous Pearl
Shopping Center in
Shanghai, China.

c

The diamond pendant in this necklace in the Smithsonian
Institution is the 68-carat Victoria Transvaal diamond from South Africa.

a