Regents Earth Science
Igneous Rock ID Lab
Mr. Williams
Geology Rox!
Name________________________________
Per________
INTRODUCTION:
All igneous rocks were formed by the solidification of molten magma or lava. There are 2 main types of
igneous rocks. One type, called Volcanic or Extrusive, contains VERY small crystals because the molten
rock cooled too quickly at or near the surface of Earth. This quick cooling does not give crystals enough
time to grow large – large enough for you to actually see them with your naked eye.
Another type, called Plutonic or Intrusive, contains larger crystals. This is because they have been able to
cool and solidify slowly, deep underground. THE SLOWER THE MAGMA COOLS, THE LARGER THE
CRYSTALS CAN GROW AND THE MORE COARSE THE TEXTURE WILL BE.
Igneous rox are classified on the basis of their CRYSTAL SIZE and their MINERAL COMPOSITION. Refer
back to your IGNEOUS ROX NOTES, as you will need them to complete this labby lab. You will most
definitely need your ESRT as well (page 6)
What are some OBSERVABLE characteristics that make these igneous
rox?
1) they may contain intergrown silicate crystals seen with the
naked eye (slow cooling)
2) they may be glassy (very fast cooling)
3) they may contain gas holes (vesicles)
VOCAB: Please define these words in your notebook. Thank you.
Igneous
Mafic
Intrusive
Lava
Extrusive
Magma
Felsic
Texture
Porphyritic
PROCEDURE:
You are going to identify igneous rocks based on their:
1) Color – Light or Dark
2) Texture – Coarse, Fine, Glassy, Vesicular
3) Minerals that are possibly present in the rox
PLEASE REFER TO YOUR IGNEOUS ROX NOTES AND YOUR HANDY DANDY ESRT –
THEY WILL LEAD YOU TO YOUR IGNEOUS ROX INFORMATION STARDOM!
Once you complete the rock ID, answer the following questions regarding igneous rox. Enjoy, and may
the force be with you!!
1) What name is applied to a coarse-grained, felsic igneous rock? _________________________
2) What rock has the same composition as granite, but smaller crystals?______________________
3) Name a coarse grained, dark colored igneous rock. ______________________________
4) What feature of pumice and scoria make them vesicular?
______________________________________________________________________________
______________________________________________________________________________
5) What 2 rock types are neither felsic nor mafic? (These 2 rocks have an intermediate composition
and color)._______________________________ and __________________________________
6) How do the 2 kinds of rock in question 5 differ from one another?
______________________________________________________________________________
__________________________________________________________
7) With respect to Earth’s surface, where do extrusive rocks cool and crystallize (that is, where do
they solidify)?
______________________________________________________________________________
___________________________________________
8) What is the texture of the very finest grained igneous rocks called?________________________
9) What do gabbro and basalt have in common?
______________________________________________________________________________
___________________________________________________________
10) How can you tell that gabbro crystallized deeper underground than basalt did?
______________________________________________________________________________
______________________________________________________________
WHEW! Well done. Now, please read the passage on the next page and
answer the questions that follow. We already learned this, so it shouldn’t
be a problem. Now go to it.
IGNEOUS ROX ID CHART
Sample
Number
Color(Light or
Dark)
Grain
Size/Texture
(coarse, fine,
glassy, vesicular)
1
2
3
4
5
6
7
8
9
Minerals Possibly
Present in Rock (use
your ESRT!)
Rock Name
10
11
12
USE THE LOWER PORTION (the minerals part) OF YOUR ESRT TO ANSWER THESE QUESTIONS!!
11) What minerals are usually found in granite?
_______________________________________________________________
12) What is the percentage of plagioclase in a typical granite? _______________
13) a) List the 4 minerals usually found in basalt and then b) write the percentages of each.
MINERAL NAME
PERCENTAGE (%)
1
2
3
4
14) What 2 minerals tend to be found in the greatest range of igneous rocks? That is…which ones
are the most common? ____________________________ and __________________________
15) What igneous rock is generally composed of just 1 mineral? _________________________
16) Unlike some other rocks, igneous rocks such as granite and gabbro are NEVER composed of
rounded rock “fragments”. What are igneous rocks composed of?
______________________________________________________________________________
_______________________________________________________________
17) Do igneous rocks usually have a layered texture? YES or NO (circle one)
18) What coarse grained igneous rock is similar in composition to basalt? _____________________
19) What is the difference between granite and rhyolite?
______________________________________________________________________________
_____________________________________________________________
20) Unlike other kinds of rocks, igneous rocks form from what substance?
______________________________________________________________________________
________________________________________________________