Igneous Rock Lab
Name: ___________________________________
Hour: ____________ Date: _________________
Reference: Use your textbook and class notes for help in completing.
Problem: How are rock characteristics used to classify igneous rocks as intrusive/extrusive & granitic/basaltic?
Background: Igneous rocks form from the cooling of molten material (magma/lava). Intrusive rocks form
under the surface and cool very slowly which produces large crystals/mineral grains. Extrusive rocks form
above the surface and cool quickly which produces small to no crystals/mineral grains. Igneous rocks can also
be classified according to chemical composition. Granitic rocks are generally light in color and made mostly out
of aluminum. Basaltic rocks are darker and are mainly composed of magnesium and iron.
Hypothesis:
Procedure:
1. Observe the mineral crystals/grains in the rock and identify it as intrusive or extrusive (circle your
answer) and EXPLAIN your answer
2. Observe the color of the rock and identify the magma/lava type it formed from (basaltic, andesitic or
granitic – circle your answer) and EXPLAIN your answer
3. Use the table/pictures on the handout to name the rock based on the results of steps 1 and 2
4. After looking at all the rocks, answer the 2 conclusion questions
Rock #1
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #2
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #3
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #4
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #5
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #6
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #7
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #8
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Rock #9
1. Intrusive or extrusive? How do you know? ________________________________________
2. Basaltic, andesitic or granitic? How do you know? __________________________________
3. Name of rock __________________________
Conclusion Questions
1. Why do intrusive igneous rocks have large mineral grains but extrusive igneous rocks have
small mineral crystals/grains?
2. Why are basaltic igneous rocks dark and granitic igneous rocks light in color?