Page 467 - 9780077418427.pdf

/Users/user-f465/Desktop
tiL12214_ch17_433-454.indd Page 444 9/3/10 6:20 PM user-f465
tiL12214_ch17_433-454.indd Page 444 9/3/10 6:20 PM user-f465 /Users/user-f465/Desktop

A Closer Look

Asbestos
sbestos is a common name for any of
Aseveral minerals that can be separated
into fireproof fibers, which will not melt
or ignite. The fibers can be woven into a
fireproof cloth, used directly as fireproof
insulation material, or mixed with plaster or
other materials. People now have a fear of all
asbestos because it is presumed to be a health
hazard (Box Figure 17.1). However, there are
about six commercial varieties of asbestos.
Five of these varieties are made from an am-
phibole mineral and are commercially called
brown and blue asbestos. The other variety is
made from chrysotile, a serpentine family of
minerals, and is commercially called white
asbestos. White asbestos is the asbestos
mined and most commonly used in North
America. It is only the amphibole asbestos
(brown and blue asbestos) that has been
linked to cancer, even for a short exposure
time. There is, however, no evidence that
exposure to white asbestos results in an
increased health hazard. It makes sense to
ban the use of and remove all the existing
BOX FIGURE 17.1 Did you know there are different kinds of asbestos? Are all kinds of
amphibole asbestos from public buildings. It asbestos a health hazard?
does not make sense to ban or remove the
serpentine asbestos since it is not a proven
health hazard.

by moving water and are deposited as sediments. Sediments are
EXAMPLE 17.4
accumulations of silt, sand, or other materials that settle out of
Based on Figure 17.13, what is the range in percentage of each mineral water. Weathered rock fragments and dissolved rock materials
in basalt? (Answer: pyroxene: 50% to 100%; calcium-rich plagioclase: both contribute to sediment deposits (Table 17.3).
0% to 50%)
Weathered rock fragments are called clastic sediments
after a Greek word meaning “broken.” Clastic sediments accu-
mulated from rocks that are in various stages of being broken
CONCEPTS Applied
TABLE 17.3
Collect Your Own
A classification scheme for sedimentary rocks
Make a collection of rocks and minerals that can be found
in your location, showing the name and location found for Sediment Type Particle or Composition Rock
each. What will determine the total number of rocks and Clastic Larger than sand Conglomerate
minerals it is possible to collect in your particular location? or breccia
Clastic Sand Sandstone
Clastic Silt and clay Siltstone,
claystone,
SEDIMENTARY ROCKS or shale
Sedimentary rocks are rocks that formed from particles or dis- Chemical Calcite Limestone
solved materials from previously existing rocks. Chemical reac- Chemical Dolomite Dolomite
tions with air and water tend to break down and dissolve the less Chemical Gypsum Gypsum
chemically stable parts of rocks, freeing more stable particles Chemical Halite (sodium chloride) Salt
and grains in the process. The remaining particles are transported

444 CHAPTER 17 Rocks and Minerals 17-12