Igneous Rocks Lab

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Igneous Rock Lab

Note: Remember you are responsible for graphs, charts and other items that form part of the overall summary of this topic.  You will need a copy of the Earth Science References tables.

Background: Igneous rock is one of the three (3) main types of rocks.  Igneous rock is formed by magma or lava becoming cooled and solidifying.  The rock may form with or without crystallization below the surface or on the surface of the planet.  Remember that magma is molten rock below the Earthís surface while lava is molten rock that has erupted onto the Earthís surface through a volcano or fissure (crack) in the Earthís surface.  Lava cools much more quickly than magma because it is on the surface.  Cooling rates influence the texture of igneous rocks: quick cooling will give fine grains while slower cooling will result in coarse grains.  Remember that igneous rocks are classified based on their texture and composition.

Vocabulary:

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magma - molten rock found beneath the surface of a planet.

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crystallization - the formation of solid crystals precipitating from a solution; may be melted or deposited by gas,

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intrusive - intrusive refers to igneous rock that has crystallized from molten magma below the surface of the Earth (also called plutons after Pluto the Roman God of the Underworld.)

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extrusive - extrusive refers to igneous rock that is formed from hot magma when it flows out (extrudes) onto the surface of the Earth as lava or explodes through a pyroclastic flow.

Materials: ESRT

Directions: Using the ESRTís answer the following questions:

1. What is the texture of rhyolite?

2. What is the crystal size of rhyolite?

3. Is rhyolite intrusive or extrusive?

4. Plutonic is also referred to as intrusive or extrusive?

5. Estimate the percentage of each mineral in rhyolite:

a. __________% Potassium Feldspar

b. __________% Quartz

c. __________% Biotite

d. __________% Amphibole (hornblende)

6. List the minerals in andesite.

7. What is the texture of scoria?

8. Name a fine-grained igneous rock with no quartz.

9. Name a coarse-grained igneous rock with no quartz.

10. Which mineral is present in much greater quantities in peridotite than in gabbro?

11. What is the texture of granite?

12. What is the crystal size of granite?

13. Is granite intrusive or extrusive?

14. Estimate the percentage of each mineral in gabbro:

a. __________%  Plagioclase Feldspar

b. __________%  Pyroxene

c. __________%  Olivine

d. __________%  Amphibole

e. __________%  Biotite

15. Name a fine-grained textured igneous rock with no pyroxene.

16. Name a coarse-grained textured igneous rock with no pyroxene.

17. Contrast rhyolite and basalt in the following categories:

a. density

b. color

c. percentage of Iron (Fe) & Magnesium (Mg)

d. percentage of Quartz

18. Name a felsic intrusive rock.

19. Name a light-colored plutonic rock.

20. Felsic rocks generally have a __________ color.

21. Mafic rocks generally have a __________ color.

22. Intrusive igneous rocks have large or small mineral crystals because of slow or fast cooling?

23. Name four (4) felsic igneous rocks:

a. __________

b. __________

c. __________

d. __________

24. Name four (4) mafic igneous rocks:

a. __________

b. __________

c. __________

d. __________

25. Name a plutonic mafic igneous rock.

26. Which igneous rock cooled slowly underground and contains mostly quartz and potassium feldspar?

27. How does the percentage of aluminum in an igneous rock affect its density?

28. Which igneous rock is fine-grained and has a lot of pyroxene?

29. Name a coarse-grained igneous rock composed mostly of olivine.

30. Name an intrusive, dense, dark igneous rock.

31. What two (2) characteristics are used to classify igneous rocks?

32. Where an igneous rock formed can be inferred from the rocks __________.

33. What causes the differences of texture in igneous rocks?

34. Fill in the blanks on the following chart:

Rock Name

Formed from lava or magma

Cooling Rate

(very fast, fast or slow)

Crystal Size

(non-crystalline, small, or large)

Texture

(glassy, fine, or coarse)

Rhyolite

Lava

Fast

Small

Fine

Gabbro

 

Slow

 

Coarse

Basalt

 

Fast

 

Fine

Pumice

Lava

 

Non-crystalline

 

Obsidian

 

Very fast

   

Granite

Magma

     

Diorite

       

Dunite

       

Andesite

       

Lab Notes  >