Geology Reference
In-Depth Information
precipitate minerals of economic value. These deposits may
eventually be brought to Earth's surface by later tectonic ac-
tivity. The copper ores of Cyprus are a good example of such
hydrothermal activity (see Chapter 2).
Many ore deposits result from contact metamorphism
during which hot, ion-rich fl uids migrate from igneous in-
trusions into the surrounding rock, thereby producing rich
ore deposits. The most common sulfi de ore minerals associ-
ated with contact metamorphism are bornite, chalcopyrite,
galena (lead), pyrite, and sphalerite (zinc); two common
iron oxide ore minerals are hematite and magnetite. Tin and
tungsten are also important ores associated with contact
metamorphism (Table 7.2).
Other economically important metamorphic minerals
include talc for talcum powder, graphite for pencils and dry
lubricants, and garnets and corundum, which are used as abra-
sives or gemstones, depending on their quality. In addition,
andalusite, kyanite, and sillimanite, which, as we mentioned
RESOURCES
Many metamorphic rocks and minerals are valuable natu-
ral resources. Although these resources include various
types of ore deposits, the two most familiar and widely
used metamorphic rocks are marble and slate, which, as we
discussed earlier, have been used for centuries in a variety
of ways (
◗
Figure 7.21).
◗
Figure 7.21
Slate Quarry in Wales Slate, which has a variety of uses, is the result of low-grade
regional metamorphism of shale. These high-quality slates were formed by a mountain-building
episode that took place approximately 400 to 440 million years ago in the present-day countries of
Ireland, Scotland, Wales, and Norway.
TABLE 7.2
The Main Ore Deposits Resulting from Contact Metamorphism
Ore Deposit
Major Mineral
Formula
Use
Copper
Bornite
Chalcopyrite
Cu
5
FeS
4
CuFeS
2
Important sources of copper, which is used in manufacturing,
transporation, communications, and construction
Iron
Hematite
Magnetite
Fe
2
O
3
Fe
3
O
4
Major sources of iron for manufacture of steel, which is used in
nearly every form of construction, manufacturing, transportation, and
communications
Lead
Galena
PbS
Chief source of lead, which is used in batteries, pipes, solder, and
elsewhere where resistance to corrosion is required
Tin
Cassiterite
SnO
2
Principal source of tin, which is used for tin plating, solder, alloys, and
chemicals
Tungsten
Scheelite
Wolframite
CaWO
4
(Fe,Mn)WO
4
Chief sources of tungsten, which is used in hardening metals and
manufacturing carbides
Zinc
Sphalerite
(Zn, Fe)S
Major source of zinc, which is used in batteries and in galvanizing iron
and making brass
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