Environmental Engineering Reference
In-Depth Information
Sedimentary rock
forms from sediment produced
when existing rocks are weathered and eroded into
small pieces, then transported by water, wind, or grav-
ity to downstream, downwind, or downhill sites. These
sediments are deposited in layers that accumulate over
time and increase the weight and pressure on underly-
ing layers. A combination of pressure and dissolved
minerals seeping through the layers of sediment crys-
tallizes and binds sediment particles together to form
the sedimentary rock. Examples include
sandstone
and
shale
(formed from pressure created by deposited lay-
ers of sediment),
dolomite
and
limestone
(formed from
the compacted shells, skeletons, and other remains of
dead organisms), and
lignite
and
bituminous coal
(de-
rived from plant remains).
Metamorphic rock
forms when a preexisting rock
is subjected to high temperatures (which may cause it
to melt partially), high pressures, chemically active flu-
ids, or a combination of these agents. These forces may
transform a rock by reshaping its internal crystalline
structure and its physical properties and appearance.
Examples include
anthracite
(a form of coal),
slate
(formed when shale and mudstone are heated), and
marble
(produced when limestone is exposed to heat
and pressure).
The interaction of physical and chemical processes
that changes rocks from one type to another is called
the
rock cycle
(Figure 12-6). It recycles the earth's three
types of rocks over millions of years and is the slowest
of the earth's cyclic processes. It also concentrates the
planet's nonrenewable mineral resources on which we
depend. Without the incredibly slow rock cycle, you
would not exist.
Science: Nonrenewable Mineral Resources
Mineral resources are nonrenewable materials
that we can extract from the earth's crust.
A
nonrenewable mineral resource
is a concentration
of naturally occurring material in or on the earth's
Erosion
Transportation
Weathering
Deposition
Igneous rock
Granite, pumice,
basalt
Sedimentary rock
Sandstone, limestone
Heat, pressure
Cooling
Heat, pressure,
stress
Magma
(molten rock)
Melting
Metamorphic rock
Slate, marble,
gneiss, quartzite
Figure 12-6
Natural capital:
the
rock cycle
is the slowest of the earth's cyclic processes. The earth's materials
are recycled over millions of years by three processes:
melting, erosion,
and
metamorphism,
which produce
ig-
neous, sedimentary,
and
metamorphic
rocks. Rock from any of these classes can be converted to rock of either
of the other two classes, or can be recycled within its own class.
