1. Igneous Rocks
What you need to know:
How do igneous rocks form?
What are the typical characteristics of igneous rocks?
How does rate of cooling affect the size of the crystals in igneous rocks?
Question: Which of the following rocks is the odd one out?
granite sandstone pumice basalt

2. Read the Cooling Rate and Crystal Size worksheet
Copy and complete the following notes, unscrambling the jumbled-up words:
Igneous rocks are formed when LOMNET rock (VAAL or GAMMA) cools so that it becomes freezes and becomes DOLIS
Igneous rocks usually contain lots of interlocking SRYCSLAT, which makes them RAHD and NOGRTS
The word igneous come from ‘ignis’ – the Latin word for RIFE
Read the Cooling Rate and Crystal Size worksheet

3. Read the Cooling Rate and Crystal Size worksheet
Igneous rocks are formed when molten rock
(lava or magma) cools so that it becomes freezes and becomes solid
Igneous rocks usually contain lots of interlocking crystals, which makes them hard and
strong
The word igneous come from ‘ignis’ – the Latin word for fire
Read the Cooling Rate and Crystal Size worksheet

4. Collect a tube of salol and a warm slide from the water bath
glass slide
Collect a tube of salol and a warm slide from the water bath
(Check that the salol has completely melted)
salol
85C water bath
2. Wipe your slide dry
3. Using a clean pipette, place a drop of salol on your slide
4. Examine the wax with a hand lens as it cools.
Record your observations
Repeat with a glass slide at room temperature and one from the cool box

5. Did the salol cool fast or slow? Are the crystal large or small?
Results:
Slide
Did the salol cool fast or slow?
Are the crystal large or small?
Hot
Room Temp.
Cold
Slow
Large
Faster
Medium
Very Fast
Small
Conclusion:
How does cooling rate affect the size of the crystals?
The faster the salol cools the smaller the crystals
OR the slower the salol cools the larger the crystals

6. Copy the diagram below
Lava flow A
Volcano
Old lava flow B
Magma
chamber C
Questions:
1. Where would the rock with the largest crystals form (A, B or C)? Explain your answer.
2. What is the difference between lava and magma?

7. What have we learnt?
How do igneous rocks form?
What are the typical characteristics of igneous rocks?
How does rate of cooling affect the size of the crystals in igneous rocks?
Igneous rocks form when molten lava/magma cools to form solid rock
Igneous rocks are hard with interlocking crystals
The faster the lava/magma cools the smaller the crystals in the rock