Name ___________________________
Date ___________Period_____
Cooling Rate (s) Vs. Crystal Size
Vocabulary: magma, lava, mineral, crystal, crystallization, igneous rock, extrusive rock,
intrusive rock
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●
●
●
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magma- molten rock below the crust
lava - molten material on surface of crust
atom - the smallest particle of all matter.
crystal - a solid in which the atoms are arranged in a repeated pattern.
crystallization -The process by which atoms are arranged to form a material with a
crystal structure
● igneous rock - rock formed from the cooling and crystallization of magma or lava.
● extrusive igneous rock - igneous rock that forms from cooling and crystallization of
lava on the surface of Earth
● intrusive igneous rock - igneous rock that forms below the surface from cooling and
crystallization of magma.
Focus Question: How does the cooling rate of molten material affect the size of mineral
crystals in igneous rock?
Hypothesis:
If the cooling rate of molten material is _____________then the size of the crystals will be
____________. If the cooling rate is ____________ then the crystal size will be
____________.
Justification:
Materials for each group: 2 Microscope slides, Salol, 1 votive candle, matches, goggles,
magnifying lenses, crushed ice, paper, pencil, small container for ice, stop watch
Procedure for growing crystals:
(Room Temp)
1. Place 3-5g of Salol in the center of 1 glass microscope slide. Spread out evenly in a small circle.
2. Heat the Salol by holding the slide about 2 cm above the flame and gently moving the slide back and forth. When Salol is
ALMOST completely melted, remove from the flame and place it on the desk and start the stop watch. (Blow Candle Out)
3. Observe for crystallization and record the time (s) when the first sign of crystallization occurs in Table 1.
4. Continue to record time (s) until all of the melt is crystallized and record the end time (s) in Table 1.
5. Calculate the elapsed time (s) from melt to crystallization (end time-start time) and record.
6. Use the hand lens and /or microscope to observe the size and shape of the crystals and sketch what you see in Table 1. Write
additional qualitative observations below data table.
7. Sketch and label the relative shape and size of the crystals in Table 1
and then place this slide aside.
(Ice bath)
1. Repeat step 1 above with the second slide.
2. Repeat step 2, but when the Salol is ALMOST melted gently place it on top of the ice bath to cool and start stop watch.
3. Repeat steps 3 – 7.
Data:
Cooling
Environment
Crystal Size vs. Cooling Rate(s)
Start Time(s) End Time(s)
Elapsed
(when first
(Salol
Time(s)
crystal
completely
(end time appeared)
crystallized)
start time)
Crystal Size
(Sketch and label key
features)
Room
Temperature
Cool
Temperature
(Ice Bath)
Table 1
Additional Qualitative Observations:
Explain: Analysis and Conclusion Follow up Questions
1. Identify the material in the experiment to what it represents in geology:
_____Solid Salol from room temp
a. Molten (melted) rock
cooling
_____ Solid Salol from ice bath cooling b. Solid intrusive igneous rock
_____Candle flame
c. Quick cooling form Lava on the surface
_____Melted Salol
d. Slow cooling from a magma chamber below the
surface
_____Ice bath cooling
e. Solid extrusive rock
_____Room temperature cooling
f. Heat from the interior of the Earth
2. Refer to the cooling rates (elapsed time) for the Salol samples. How do these
differ? Use specific information from the data to support this answer.
3. Observe the mineral crystals on each slide. Describe how each looks. How are
the crystals similar and different in appearance?
4. Refer to you hypothesis about the relationship between cooling rate and crystal
size. Was your educated guess supported by the data from this activity?
Explain using specific information from the data.
5. Below are the pictures of the igneous rocks from the Mystery Samples. Using
background information & the knowledge gained through this activity,
explain in detail why the two rocks have different sized mineral crystals. (Use
the vocabulary words: Lava, magma, intrusive and extrusive, crystallization,
crystals in explanation)
Figure 1 Igneous rock sample 6 with large mineral Figure 2 Igneous rock sample 1 with small mineral
crystals.
crystals.
6. Explain at least 2 ways this model of crystallization is similar to the process of
crystallization in igneous rocks and at least 2 ways that it is different.