Rocks 4 – Metamorphic (6.4)
Metamorphic rocks come from rocks that already exist. We call those existing rocks
_parent_ __rock_
The three factors that affect metamorphism are:
o __heat__
o __pressure__
o __moisture__
What natural forces may provide the heat and pressure necessary for metamorphism to
happen?
Earth’s internal heat, the weight of overlying rocks, and the deformation of rock as mountains build
As metamorphism takes place, what happens to the minerals of the parent rock?
enlarged
Re-formed
New minerals may appear
Why would a metamorphic rock typically be denser and less porous than its parent?
Pressure forces the grains/crystals closer together
Compare and Contrast Regional & Local (Contact) Metamorphism
How it occurs:
Sketch what the process
may look like: Page 239
may help for the Regional
sketch
Regional
Local (Contact)
Happens during mountainbuilding movements of the
crust, when large areas of rock
change form after exposure to
intense heat and pressure;
occurs over very large areas
Happens when hot magma moves
into a rock, heating and changing
it; occurs in smaller, more
distinct areas
Rock
Quartzite
Description
Parent
Consist largely of quartz
crystals. Dense non-foliated,
uniformly crystalline rock
Sandstone
Marble
Usually non-foliated and evengrained with a sugar-like texture
Limestone
Slate
Slightly shinier and has a flatter,
less irregular surface
Shale
Schist
Tend to be large-grained and
often contain large crystals of
minerals not found in the parent
rock
Gneiss
The name of the gneiss
describes its chemical
composition. Has the coarsest
foliation of all the metamorphic
rocks
Shale and Basalt
Granite
Using page 137, what would be a good description for the term “foliation”?
Wavy parallel bands of the same mineral throughout the rock
On page 149 the steps in the coal formation process are shown.
o What process must take place to transform bituminous coal into anthracite coal?
Heat and pressure from regional metamorphism
o Which would be better to burn for energy?
Anthracite because bituminous coal contains up to 85% carbon, while anthracite
contains about 90-95% carbon
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