The Rock cycle

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The Rock cycle
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Igneous rocks

• A rock "sight-seeing" tour around the world
  might well begin in the Hawaiian Islands with a
  visit to the world's most active and best-studied
  volcano, Kilauea. This famous volcano, like
  others across the globe, is the birthplace of
  thousands of tons of rocks.

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• The rocks are "born" as volcanic eruptions eject
  massive amounts of magma onto Earth's surface.
  Remember that magma is nothing more than a large
  body of hot liquid rock and minerals. As the
  magma cools into a solid rock around the base of
  the volcano, it can be collected as samples of
  rocks such as basalt, pumice, or obsidian.

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Mount Rushmore is made of Granite
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Metamorphic rock

• What does it mean to be "rock solid?" The phrase
  is used to describe something that cannot easily
  be changed. But metamorphic rocks are rocks that
  have been changed within the Earth. Because rocks
  are not easily changed, metamorphic rocks must
  develop in environments where heat and pressure
  are intense and extreme. These extreme conditions
  are only present deep inside the Earth.

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Contact Metamorphism

• CONTACT METAMORPHISM occurs when a rock is
  exposed to hot magma inside the Earth. The
  intense heat of the magma alters the rock, often
  causing its minerals to recrystallize. Thus, the
  new rock has new or larger mineral crystals than
  the older rock. Sometimes, the hot magma will
  even introduce new minerals and modify the entire
  chemical composition of the original rock. The
  area of rock affected by contact metamorphism is
  appropriately known as the baked zone.

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Regional Metamorphism

• REGIONAL METAMORPHISM, on the other hand, occurs
  during the formation of mountain ranges. As
  tectonic plates collide and converge, intense
  pressure deforms and alters sedimentary and
  igneous rocks already buried in the Earth. The
  mountain ranges of east Greenland are an example
  of where this has taken place. Often, folds or
  curves in the rocks indicate the direction of the
  intense pressure.

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Sedimentary Rock

• Traveling east to Zion National Park in Utah,
  tourists would find the well-known Navajo
  Sandstone Formation. It looks like a towering
  sand dune that has been permanently solidified
  against the landscape. The sandstone rocks that
  make up the Navajo Sandstone Formation began
  millions of years ago as tiny grains of sand in a
  prehistoric desert. Over time, winds carried the
  sand and deposited it into giant sand dunes. The
  pressure of each new sand deposit caused the sand
  underneath to compact and cement together into
  solid rock.

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Sedimentary Rock
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shale

• A common clastic sedimentary rock is shale, the
  most abundant of all sedimentary rocks. Shale
  forms when mud and clay harden. Because the clay
  sediments are extremely small, they settle out
  slowly. In fact, shale formations can take about
  5 million years to form.

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limestone

• The most common chemical sedimentary rock is
  limestone. Most limestone rocks are organic
  that is, they develop from the remains of
  organisms. Much limestone is made up of marine
  animals and contains pieces of shells, corals,
  and mollusks. Another chemical sedimentary rock
  is coal, which is often found in layers with
  other sedimentary rocks. As plant remains are
  deposited in layers and slowly alter into carbon
  over millions of years, they form coal.

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Limestone cliffs , limestone with fossils
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• Although these sandstone rocks began as a
  collection of individual grains of sand, the sand
  grains themselves had to come from somewhere and
  something else. Where might these sand grains may
  have originated?

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• Geologists theorize that the sand grains may have
  broken off a larger rock formed earlier by a
  volcanic eruption. Or they may have broken off
  older sandstone rocks. Because the Earth is so
  dynamic, rocks are always changing. Minerals that
  make up rocks are constantly moved and acted upon
  by the environment. Environmental agents change
  one type of rock into an entirely new rock. The
  web of environmental processes that forms and
  changes rocks is known as the ROCK CYCLE.

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The Rock Cycle
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Another view of the Rock Cycle
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Rock cycle

• To gain an idea of how the rock cycle works, the
  world rock tour that began in Hawaii might end in
  east Greenland. Millions of years ago there,
  magma deep inside the Earth forced its way into
  another rock and solidified. This created an
  igneous rock. Then, intense pressure in the Earth
  caused the rock to up-heave, fold, and crumple,
  until it became an entirely new rock a
  metamorphic rock. That new rock now makes up a
  mountain formation in Greenland.

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Activity

• The rock cycle never ends.
• I, Rock Sandy Stone said to her son,
  "Rocky, I remember when you were just a cute
  little grain of sand..." Tell the story of a
  rock's progression through the rock cycle.