118 The History of the Earth: Supplemental Guide 6A | The Three Types of Rocks
Show image 6A-15: Limestone to marble
If limestone is subjected to intense pressure for an even longer
period of time, it can turn into another kind of rock called marble.
Marble is very hard, and it often has a beautiful, pure white
color. People have used marble for thousands of years to make
fi ne buildings and sculptures.
Marble is known as a metamorphic rock, which is the third and
least common type of rock.^19 Metamorphic comes from the Greek
word for transformation, or change. Metamorphic rocks are formed
when other types of rocks undergo intense heat and pressure and
change, or metamorphose, into new kinds of rocks.^20
Show image 6A-16: Three types of rock
Congratulations! You are becoming a geologist! Now you
know about the three rock types: igneous, sedimentary, and
metamorphic. Won’t everyone be impressed when you tell them
about the new words you learned?Discussing the Read-Aloud 15 minutes
Comprehension Questions 10 minutes
- Literal What are the three types of rocks? (The three types of
rocks are metamorphic, sedimentary, and igneous.) - Inferential How are igneous rocks formed? Remember:
igneous means “fi re.” (Igneous rocks are formed from hot
magma or lava that cools and hardens.) - Inferential How are sedimentary rocks formed? (Sediments
settle and form a thick sludge on the bottom of a lake that
thickens over time. The pressure from the weight of the
sediments makes it harden into sedimentary rocks.) - Inferential How are metamorphic rocks formed? (Metamorphic
rocks are formed when heat and pressure change igneous and
sedimentary rocks into new rocks.)
19 Whenever you hear the word
metamorphic, hold out both
hands and then clasp them tightly
together.
20 What’s the third type of rock,
formed when heat and pressure
change igneous and sedimentary
rocks into new kinds of rocks?