Melted rock is the original source material for all rocks on the Earth’s surface.
The source material for all rocks on the Earth’s surface originally comes from the Earth’s interior. Molten rock is called magma when it is still in the Earth’s interior, and lava when it reaches the Earth’s surface. A number of processes then determine the final form and composition of the rock. Geologists have categorized rocks into three main types based principally on how they are formed.
- Igneous Rock: Igneous rock forms when magma or lava cools and hardens.
- Sedimentary Rock: Wind, water, ice, or gravity can break rock into smaller fragments, or gradually erode it over time. These loose fragments are known as sediment. Sedimentary rock results when sediment is compacted and cemented together over time.
- Metamorphic Rock: Igneous or sedimentary rock can change when subjected to extreme heat or pressure. The resulting rock is called metamorphic rock.
Intense pressure can change the igneous rock granite into the metamorphic rock gneiss.
Did You Know?
Rock Luggage
The six Apollo missions that landed on the moon between 1969 and 1972 returned with a total of 382 kg (approximately 850 pounds) of moon rocks.
Word Link
Igneous: This word dates from 1664, and is based on the Latin word igneus which means fire.
Sedimentary: This adjective was first used in the term sedimentary rock in 1839. It is based on the 1547 noun sediment which is derived from the Latin word sedimentum which means settling.
Metamorphic: This adjective dates from 1816. It is based on the 1533 English noun metamorphosis which is taken directly from the Latin word metamorphosis which means to transform.
Try This!
What Lies Beneath
The main view to the right illustrates the location of the main rock types in North America.
- Examine the legend carefully.
- What color corresponds to each of the three main rock types? Purple corresponds to metamorphic rock, blue to sedimentary rock, and yellow or beige to igneous rock.
- Click here to zoom in on North America and to add in the state / provincial boundaries.
- In the United States, what is the dominant rock type in:
- What states in the contiguous U.S. have significant amounts of metamorphic rock? New York and Virginia have significant amounts of metamorphic rock.
- In Canada, what is the dominant rock type in:
- Zoom in on the state or province where you currently live.
- List all the rock types that are found in your home state / province. Answers will vary depending on location.