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The Rock Cycle
“Review”
Igneous Rocks
Igneous: produced under conditions involving intense heat
• Igneous rocks are called fire rocks and are formed
either underground or above ground. Underground,
they are formed when the melted rock, called
magma, deep within the earth becomes trapped in
small pockets. As these pockets of magma cool
slowly underground, the magma becomes igneous
rocks.
• Igneous rocks are also formed when
volcanoes erupt, causing the magma
to rise above the earth's surface. When
magma appears above the earth, it is
called lava. Igneous rocks are formed
as the lava cools above ground.
Sedimentary rock
Sediment: “the matter that settles to the bottom of a liquid”
• For thousands, even millions of years, little pieces of
our earth have been eroded--broken down and worn
away by wind and water. These little bits of our earth
are washed downstream where they settle to the
bottom of the rivers, lakes, and oceans.
• Layer after layer of eroded earth is deposited on top
of each.
• These layers are pressed
down more and more through
time, until the bottom layers
slowly turn into rock.
Metamorphic Rocks
meta: prefix “changed, altered”
morph: to transform or be transformed completely in appearance or character
• Metamorphic rocks are rocks that have "morphed"
into another kind of rock. These rocks were once
igneous or sedimentary rocks. How do sedimentary
and igneous rocks change?
• The rocks are under tons and tons of pressure,
which fosters heat build up, and this causes them to
change. If you exam metamorphic
rock samples closely, you'll discover
how flattened some of the grains in
the rock are.
Mineral Formation
What is a mineral?
• Mineral- a naturally occuring substance with a
characteristic chemical composition expressed
by a chemical formula; may occur as individual
crystals (which diamonds are) or may be
disseminated in some other mineral or rock
• Rock- a consolidated or unconsolidated
aggregate of mineral grains consisting of one or
more mineral species and having some degree
of chemical and mineralogic constancy
Formation of Minerals
• The Earth has a solid core of iron and nickel surrounded by a mantle
of molten rock. When this material forces itself into many cracks and
other points of weakness in the crust, it is called magma. These
tongues of molten rock, which move out in many directions, heat the
surrounding rock, altering it and, in some cases, causing it to remelt. The whole mass then cools and that is when minerals, some of
which are valuable, begin to crystallize.
• Mineral constituents of molten lava crystallize at different
temperatures. As a result, they tend to concentrate during the
cooling process. It is these concentrations that often form mineral
deposits. As each different mineral crystallizes out of the magma,
the composition of the magma changes. Heavier metals sink to the
bottom of the semi-liquid mass and are concentrated in a process
called magmatic segregation. Some magmas have no valuable
minerals, while others contain economically exploitable mineral
deposits.
Ore
• Ores are minerals that contain metals in
large amounts. A mineral is called an ore if
a metal can be extracted or separated
easily, and in large amounts to be sold at a
profit.