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TABLE 17.1

Classification scheme of some common minerals
MINERALS

Silicates Nonsilicates

Carbonates Sulfates
Ferromagnesian Clay Minerals Calcite Gypsum
Dolomite Anhydrite
Biotite Kaolinite
Hornblende Illite
Augite Chlorite Oxides Sulfides
Olivine Hematite Pyrite
Nonferromagnesian Magnetite Sphalerite
Quartz Ilmenite Galena
Muscovite (white mica) Aluminum oxides Chalcopyrite
Feldspars (aluminum silicates)
Plagioclase Phosphates Halides
(sodium feldspar)
(calcium feldspar) Apatite Halite
Orthoclase (potassium feldspar) Fluorite

Native Elements
Gold
Silver
Copper
Diamonds
Sulfur

structures. There are four major arrangements of the units: to exist deep within Earth. Another interesting, less common
(1) isolated tetrahedrons, (2) chain silicates, (3) sheet silicates, and structure is found in the asbestos minerals. These minerals have
(4) framework silicates (see Figure 17.7). Other structures are a sheet silicate structure that is rolled into fiberlike strands,
possible but not as common. The impact of meteorites, for ex- resulting in a wide variety of silicates that are fibrous.
ample, creates sufficiently high temperatures and pressures to The remaining 8 percent of minerals making up Earth’s
form a silicate structure with six oxygens around each silicon crust that do not have silicon-oxygen tetrahedrons in their
atom rather than the typical four. A similar structure is believed crystal structure are called nonsilicates. There are eight sub-
groups of nonsilicates: (1) carbonates, (2) sulfates, (3) oxides,
(4) sulfides, (5) halides, (6) phosphates, (7) hydroxides, and
(8) native elements. Some of these are identified in Table 17.1.
The carbonates are the most abundant of the nonsilicates, but
others are important as fertilizers, sources of metals, and sources
of industrial chemicals.

A PHYSICAL PROPERTIES OF MINERALS
Oxygen Each mineral has its own set of physical properties because it has
a unique chemical composition and crystal structure. If a particu-
lar mineral sample happens to have formed large crystals with
well-developed shapes, it is often possible to tell one mineral from
another through identifying characteristics. There are about eight
characteristics, or physical properties, that are useful in identify-
Silicon
ing minerals. These are the characteristics of color, streak, hard-
B ness, crystal form, cleavage, fracture, luster, and density.
The color of a mineral is an obvious characteristic, but it is of-
FIGURE 17.6 (A) The geometric shape of a tetrahedron with
four equal sides. (B) A silicon and four oxygen atoms are arranged ten not very useful for identification. While some minerals always
in the shape of a tetrahedron with the silicon in the center. This is seem to appear the same color, many will vary from one specimen
the basic building block of all silicate minerals. to the next. Variation in color is usually caused by the presence

17-5 CHAPTER 17 Rocks and Minerals 437