Page 89 - Laboratory Manual in Physical Geology

ACTIVITY true minerals normally form by inorganic processes, some
organisms make them as shells or other parts of their bodies.
3.1 Mineral and Rock Inquiry These so-called biominerals are of obvious organic origin
(made by plants and animals). Examples include aragonite
mineral crystals in clam shells and tiny magnetite crystals
THINK What are minerals and crystals, and how in the human brain. People make cultured mineral crystals
About It are they related to rocks and elements? in laboratories. Their chemical and physical properties are
identical to naturally-formed mineral crystals, but they are
OBJECTIVE Analyze rock samples, and infer how not true minerals because they are synthetic (man-made,
minerals are related to and distinguished from rocks, not natural).
crystals, and chemical elements.

PROCEDURES How Are Minerals Classified?
1. Before you begin , do not look up defi nitions and Geologists have identified and named thousands of different
information. Use your current knowledge, and kinds of minerals, but they are often classified into smaller
complete the worksheet with your current level groups according to their importance, use, or chemistry.
of ability. Also, this is what you will need to do For example, a group of only about twenty are known as
the activity: rock-forming minerals , because they are the minerals that
make up most of Earth’s crust. Another group is called the
____ Activity 3.1 Worksheet (p. 101 ) and pencil
,
industrial minerals because they are the main non-fuel
2. Then answer every question on the worksheet raw materials used to sustain industrialized societies like
in a way that makes sense to you and be ours. Some industrial minerals are used in their raw form,
prepared to compare your ideas with others.
such as quartz (quartz sand), muscovite (used in computer
3. After you complete the worksheet , read about chips), and gemstones. Most are refined to obtain specific
minerals and rocks below and be prepared to elements such as iron, copper, and sulfur. All minerals are
discuss your observations, interpretations, and also classified into the following chemical classes:
inferences with others.
■ Silicate minerals are composed of pure silicon dioxide
4-
(SiO , called quartz) or silicon-oxygen ions (SiO )
4
2
combined with other elements. Examples are olivine:
Minerals and Rocks (Fe, Mg) SiO , potassium feldspar: KAlSi O , and
4
2
8
3
kaolinite: Al (Si O )(OH) .
8
10
4
2
Many people think of minerals as the beautiful natural 2-
■ Oxide minerals contain oxygen (O ) combined with
crystals mined from the rocky body of Earth and displayed
a metal (except for those containing silicon, which
in museums or mounted in jewelry. But table salt, graphite
are silicate minerals). Examples are hematite: Fe O ,
2
3
in pencil leads, and gold nuggets are also minerals.
magnetite: Fe O , and corundum: Al O .
3
3
2
2
-
■ Hydroxide minerals contain hydroxyl ions (OH)

What Are Minerals?
combined with other elements (except for those
According to geologists, minerals are inorganic, naturally containing silicon, which are silicate minerals).
occurring solids that have a definite chemical composition, Examples are goethite: FeO(OH) and limonite:
#
distinctive physical properties, and crystalline structure. In FeO(OH) nH O.
2
2-
other words, each mineral ■ Sulfide minerals contain sulfur ions (S ) combined

■ occurs in the solid, rocky body of Earth, where it formed with metal(s) and no oxygen. Examples are pyrite:
by processes that are inorganic (not involving life). FeS , galena: PbS, and sphalerite: ZnS. When they are
2
■ has a definite chemical composition of one or more scratched or crushed, one can usually smell the sulfur

chemical elements that can be represented as a chemi- in these minerals. 2-
cal formula (like NaCl for halite, FeS for pyrite, and ■ Sulfate minerals contain sulfate ions (SO ) com-
4
2
Au for pure “native gold”). bined with other elements. Examples include gypsum:
#
■ has physical properties (like hardness, how it breaks, CaSO H O and barite: BaSO .

4
2
4
and color) that can be used to identify it. ■ Carbonate minerals contain carbonate ions
2-
■ has crystalline structure—an internal patterned (CO ) combined with other elements. Examples

3
arrangement or geometric framework of atoms that can include calcite: CaCO and dolomite: CaMg(CO ) .
3 2
3
be revealed by external crystal faces ( FIGURES 3.1A , B ), These minerals react with acid, the way baking
the way a mineral breaks ( FIGURE 3.2B ), and in atomic- soda (which is the mineral named nahcolite and the
resolution images ( FIGURE 3.2C ). chemical compound named sodium bicarbonate:
NaHCO ) reacts with acetic acid (CH COOH) in
3
3
A few “minerals,” such as limonite (rust) and opal vinegar. Geologists use dilute hydrochloric acid (HCl)
( FIGURE 3.3 ) never form crystals, so they do not have to detect carbonate minerals because the reaction

crystalline structure. They are mineral-like materials makes larger bubbles. If a mineral reacts with the
( mineraloids ) rather than true minerals. And even though all dilute HCl, then it is a carbonate mineral.
74 ■ L ABOR ATORY 3