Download Ch 5 Sec 5: Metamorphic Rocks

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Ch 5 Sec 5: Metamorphic Rocks
Guide for Reading
■ Under what conditions do metamorphic rocks form?
■ How do geologists classify metamorphic rocks?
■ How are metamorphic rocks used?
Every metamorphic rock is a rock that has changed its form. In
fact, the word metamorphic comes from the Greek words meta,
meaning “change,” and morphos, meaning “form.”
Heat and pressure deep beneath Earth’s surface can change any
rock (igneous, metamorphic or sedimentary) into metamorphic
rock.
When rock changes into metamorphic rock, its appearance, texture,
crystal structure, and mineral content change.
Collisions between Earth’s plates can push rocks down toward the
heat of the mantleMagma rising through the crust can also
provide heat to produce metamorphic rocks Rock buried deep in
the crust is under pressure hundreds or thousands of times greater
than at Earth’s surface that pressure can squeeze rock so tightly
the mineral crystals change rock into metamorphic rock.
When metamorphic rock is forming, high temperatures can change
the size and shape of grains in the rock. Tremendous pressure
which increases as you go deeper below the Earth’s surface can
also squeeze rock so tightly that the mineral grains may line up in
flat, parallel layers.
Geologists classify metamorphic rocks according to the
arrangement of the grains that make up the rocks.
Metamorphic rocks that have their grains arranged in parallel
layers or bands are said to be foliated. Foliated rocks—
including slate, schist, and gneiss—may split apart along these
bands. One common foliated rock is slate, which is basically a
denser, more compact version of shale.
Igneous Granite Metamorphic foliated Geneiss
Sedimentary Shale
Metamorphic foliated Slate
Some metamorphic rocks are nonfoliated. The mineral grains in
these rocks are arranged randomly. Nonfoliated metamorphic
rocks—including marble and quartzite—do not split into layers.
Quartzite forms out of sandstone. The weakly cemented quartz
particles in the sandstone recrystallize to form quartzite, which is
extremely hard.
Sedimentary Sandstone Metamorphic Non foliated Quartzite
Certain metamorphic rocks are important materials for
building and sculpture.
Two of the most useful metamorphic rocks are:
1. Marble can be cut into thin slabs, and it can be polished so
that its surface is smooth and mirror-like. These qualities
have led architects and sculptors to use marble for many
buildings and statues. For example, one of America’s most
famous sculptures is in the Lincoln Memorial in Washington,
D.C.
2. Like marble, slate comes in a variety of colors, including
gray, black, red, and purple. Slate, because it is foliated,
splits easily into flat pieces that can be used for flooring,
roofing, outdoor walkways, or chalkboards.