GEOLOGY is the study of the Earth and what it’s made of, including its natural history. This history is recorded in rocks and it describes how the earth is always changing and reshapes over time. The Rock Cycle highlights how three main types of rocks, SEDIMENTARY, METAMORPHIC, and IGNEOUS came to be and where they came from. Each type of rock changes conditions over time. Rocks are destroyed, melted down, and reform through various ways:
- weathering and erosion
- sedimentation and deposition
- cooling and crystallizing melting
- heat and pressure
- lithification (compacting and cementing)
Igneous rocks are formed of magma, the molten form of the earth’s mantle layer. Igneous rocks can form above ground as lava spewing from volcanoes. But igneous rocks can also form below the surface. Pockets of magma get stuck in layers of the earth.
As they get closer and closer to the surface, the magma slowly cools. Granite is an igneous rock that formed from a slow-cooling pocket of magma (rocksandminerals4u.com, 2013).
Like basalt, igneous rocks form from lava and magma.
Sedimentary rocks form from small weathered particles of other rocks or the weathered shells of sea animals. Wind and rain beating on the faces of exposed rock tend to wear off particles that are blown or washed to a new location.
When sea creatures die, the shells settle on the bottom of the ocean. As the sediments pile up, they press together to form Sedimentary rock (rocksandminerals4u.com, 2013).
Like conglomerate, sedimentary rocks form from sediment and chemical precipitation from seawater.
Metamorphic rocks form under intense heat and pressure. Metamorphic rocks start out as igneous rocks, sedimentary rocks or other types of metamorphic rocks, but through heat or pressure, change characteristics such as sheen, tightness of grain and hardness.
Rocks continually change form. What started out as sedimentary rock may change to metamorphic and, with time and weathering, change back to sedimentary (rocksandminerals4u.com, 2013).
Like serpentinite,metamorphic rocks form from other rocks that recrystallize under higher pressures and temperatures.
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LEARN MORE: INTERACTIVES – ROCK CYCLE
LEARN MORE: THE LEARNING ZONE – ROCKS
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- Rocks are classified into one of three groups, depending on how they form. What are three rock classifications?
- What geological process is needed in order for an igneous rock to form?
- Which physical characteristic is most helpful in classifying sedimentary rocks?
- Which physical characteristic is least helpful in classifying sedimentary rocks?
- Which type of rock would you expect to be common on the floor of a large, deep lake? Why?
- Would you expect to find metamorphic rock deep in Earth’s crust? Why or why not?