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Science and Society

Using Mineral Resources
ost people understand that our mineral is too low, plants grow poorly, if at all. Most that already have adequate phosphate miner-
M resources are limited and that when agricultural soils are artificially fertilized with als. Estimates are that the worldwide existing
we use them, they are gone. Of course, some phosphate minerals. Without this amend- land area with adequate phosphate minerals
mineral resources can be recycled, reducing ment, plant productivity would decline and, will supply food for only 2 billion people on
the need to mine more minerals. For ex- in some cases, cease altogether. all of Earth. Phosphate is an essential element
ample, aluminum can be recycled and used Phosphate occurs naturally as the min- for all life on Earth, and no other element can
over and over. Glass, copper, iron, and other eral apatite. Deposits of apatite were formed function in its place.
metals can similarly be recycled repeatedly. where ocean currents carried water rich in
Other critical resources, however, cannot dissolved phosphate ions to the continen-
be recycled and cannot be replaced. Crude tal shelf. Here, phosphate ions replaced the QUESTIONS TO DISCUSS
oil, for example, is a dwindling resource that carbonate ions in limestone, forming the Discuss with your group the following
will eventually become depleted. Oil is not mineral apatite. Apatite also occurs as a questions concerning the use of mineral
recyclable once it is burned, and no new minor accessory mineral in most igneous, resources:
supplies are being created, at least not at a sedimentary, and metamorphic rocks. Some
rate that would make them available in igneous rocks serve as a source of phosphate 1. Should the mining industry be permit-
the immediate future. Even if Earth were a fertilizer, but most phosphate is mined from ted to exhaust an important mineral
hollow vessel completely filled with oil, it formerly submerged coastal areas of lime- resource? Provide reasons with your
would eventually become depleted, perhaps stone, such as those found in Florida. answer.
sooner than you might think. Trends in phosphate production and 2. What are the advantage and disadvan-
Also another of our mineral resources use suggest that the world reserves of phos- tages of a controlled mining industry?
that is critically needed for our survival will phate rock will eventually be exhausted. New 3. If phosphate minerals supplies become
eventually be depleted. That resource is phos- sources might be discovered, but eventually exhausted, who should be responsible
phorus derived from phosphate rock. Phos- phosphate rock will no longer be available for developing new supplies or
phorus is an essential nutrient required for for use as a fertilizer. When this happens, the substitutes, the mining industry or
plant growth, and if its concentration in soils food supply will have to be grown on lands governments?

of foliation is determined by the extent of the metamorphic
changes (Table 17.5). For example, slate is a metamorphic rock
formed from the sedimentary rock shale. Slate is fine-grained
with no crystals visible to the unaided eye. Alignment of the
microscopic crystals results in a tendency of slate to split into
flat sheets. Greater heat and pressure can cause greater meta-
morphic change, resulting in larger crystals and increased fo-
liation. The metamorphic rock called schist can be produced
from slate by further metamorphism. In schist, the cleavage
surfaces are now visible, and coarser mica crystals are visible
to the unaided eye. Still further metamorphism of schist may
break down the mica crystals and produce alternating bands of
light and dark minerals. These bands are characteristic of the
metamorphic rock gneiss (pronounced “nice”) (Figure 17.20).

TABLE 17.5
A classification scheme for metamorphic rocks
Metamorphic Texture Metamorphic Rock
Nonfoliated Quartzite and marble
Very finely foliated Slate
Finely foliated Schist
FIGURE 17.20 This banded metamorphic rock is very old; at
Coarsely foliated Gneiss an age of 3.8 billion years, it is probably among the oldest rocks on
the surface of Earth.

17-15 CHAPTER 17 Rocks and Minerals 447