Rocks and Minerals by UTH Rocks and Minerals by UTH    

Lesson 23: Extrusive Igneous Rocks

Directions

Study the lesson for one week.

Over the week:

• Read the lesson.
• Review the synopsis.
• Recite aloud the vocabulary words and their definitions.
• Study the rock and mineral of the week.
• Complete the enrichment activities.
• Study the review questions.

Synopsis

There are three major groups of rock that make up the crust of the Earth: igneous, metamorphic, and sedimentary. There are two subgroups of igneous rocks, those formed below the surface of the Earth (intrusive from magma) and those formed on the surface (extrusive from lava). Extrusive rocks tend to have smaller crystals than intrusive, as they cool relatively quickly on the surface of the Earth.

Vocabulary

Igneous Rock: A rock formed by the cooling of molten rock, either below the surface (intrusive) or on the surface (extrusive).
Intrusive Igneous Rock: Igneous rocks formed below the surface of the Earth from magma. The relatively slow cooling favors the development of large crystals.
Extrusive Igneous Rock: Igneous rocks formed above the surface of the Earth from lava. The relatively rapid cooling favors the formation of small crystals.

Rock or Mineral of the Week

Overview

• Obsidian is a shiny black volcanic glass.
• Obsidian, an extrusive igneous rock, forms from lava above the surface of the Earth.

Interesting Facts

• Obsidian cools so quickly it has no grains at all. Instead, the lava forms a smooth, shiny glass.
• Snowflake obsidian is a variant of obsidian that contains white cristobalite crystals that look like snowflakes.

• Obsidian breaks into sharp pieces and points and was used to make weapons and tools back in the Stone Age (circa 30,000 BCE to about 3,000 BCE). See here an obsidian arrowhead.

Enrichment

Activity 1: Narrate the Lesson

• After reading or listening to the lesson, narrate the lesson aloud using your own words.

Activity 2: Take a Nature Walk

• Embark on a nature walk.
• Collect one rock or mineral specimen.
• Use the gathered specimen to create the field book entry.

Activity 3: Complete a Field Book Entry   

After your nature walk, complete page 6 in 'Fifth Grade Science Rocks and Minerals Notebook Pages.'

Review

Question 1

What is the difference between magma and lava?

1 / 6

Answer 1

Magma is located under the Earth's surface and lava above the Earth's surface.

1 / 6

Question 2

Which rock group is formed from either cooling magma or lava?

2 / 6

Answer 2

The igneous rock group is formed from cooling magma or lava.

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Question 3

Which rock group is formed from cooling magma?

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Answer 3

The intrusive igneous rock group is formed from cooling magma.

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Question 4

Which rock group is formed from cooling lava?

4 / 6

Answer 4

The extrusive igneous rock group is formed from cooling lava.

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Question 5

Is obsidian an igneous, metamorphic, or sedimentary rock?

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Answer 5

Obsidian is an igneous rock.

5 / 6

Question 6

Is obsidian formed from lava or magma?

6 / 6

Answer 6

Obsidian is an extrusive igneous rock, so it forms aboveground from lava.

6 / 6

❮ ❯

1. What is the difference between magma and lava? Magma is located under the Earth's surface and lava above the Earth's surface.
2. Which rock group is formed from either cooling magma or lava? The igneous rock group is formed from cooling magma or lava.
3. Which rock group is formed from cooling magma? The intrusive igneous rock group is formed from cooling magma.
4. Which rock group is formed from cooling lava? The extrusive igneous rock group is formed from cooling lava.
5. Is obsidian an igneous, metamorphic, or sedimentary rock? Obsidian is an igneous rock.
6. Is obsidian formed from lava or magma? Obsidian is an extrusive igneous rock, so it forms aboveground from lava.

References

'Obsidian.' Wikipedia. en.wikipedia.org/wiki/Obsidian. n.p.

Cited Physical Properties. Geology.com. geology.com/rocks. n.p.