CHAPTER 3: ROCKS
THE BIG IDEA: Rocks change into other rocks over time.
THE KEY CONCEPT: The rock cycle shows how rocks change.
1. rock- a naturally formed solid that is usually made up of one or more types of minerals
2. rock cycle- the set of natural processes that form, change, break down and re-form rocks
MOST ROCKS ARE MADE OF MINERALS
· Just as letters combine to make up words, minerals combine to make up rocks.
· A mineral is always made up of the same proportions of the same minerals. They always have a crystal structure.
· Most rocks, though, are made up of different amounts of different minerals.
· Some rocks are made up of one kind of mineral, and some rocks contain no minerals at all. Limestone is composed entirely of calcite and obsidian contains no minerals at all. Coal is another rock that contains no minerals.
OUR WORLD IS BUILT OF ROCKS
· Earth is built almost entirely of rocks.
· What do you see when you look at the Earth’s surface?
· Realize that this is a very thin covering of the planet (crust).
· Between the crust and the metallic core, the Earth is made of solid and molten rock.
· Because rocks are so common, they are used for many things.
- Buildings (houses and skyscrapers)
- Sources of metals (Fe, Al, Cu)
- Statues and other art
- Base for pavement (roads and highways)
· Granite blocks form parts of the Great Wall of China.
· Limestone blocks form the Great Pyramid in Egypt.
· Carved granite is the base of the faces of Mount Rushmore.
· People study rocks to learn how areas have changed through time.
- May show that North America has been buried under ice many times.
- Geologic maps show types of rocks and where they’re located.
ROCKS CHANGE AS THEY MOVE THROUGH THE ROCK CYCLE
· A cycle is made up of repeating events that happen one after the other.
· Rock cycle animation
· Rocks do not always move through the cycle in a particular order, though. (Rock cycle transparency)
· Like all cycles, the rock cycle has no beginning or end. It is continuous.
1) Igneous rock
· Forms when molten rock cools and becomes solid
· Can form within the Earth or on the surface
· Can form deep within the earth and then reach the surface over time (erosion or during mountain forming)
2) Sedimentary rock
· Forms when pieces of older rocks, plants and other loose materials get cemented together
· Loose materials are carried by water or wind and settle into layers
· Lower layers get pressed by weight of upper layers
· New minerals can act as a glue to hold the rock together
· Some form in other ways, like when water evaporates leaving minerals behind
3) Metamorphic rock
· Forms when heat or pressure cause older rocks to change into new types of rock
· Rocks buried deep in the crust are exposed to greater temperatures. This causes minerals to change into new minerals. The rock becomes metamorphic.
· May be raised to the surface over time.
ROCKS IN THE CRUST
· 95% of the crust is metamorphic and igneous rock.
· 5% is sedimentary rock.