Igneous Rocks

​Igneous Rocks

Multiple Choice

How are igneous rocks formed?

• From the cementation and compaction of sediments.

• By the erosion of sediment.

• By the melting of existing rocks under pressure.

• From the cooling and solidification of molten rock.

Open Ended

Compare magma and lava.

Remember that 'compare' means give a similarity and a difference.

Intrusive igneous rocks have formed by the cooling of magma.

Some examples are:
Granite, Diorite, and Gabbro

​​Intrusive

Extrusive igneous rocks have formed by the cooling of lava.

Some examples are:
Basalt, Obsidian, and Pumice

​​Extrusive

Multiple Choice

Pegmatite is another type of intrusive igneous rock. Where is pegmatite most likely to be found?

• On the surface of a volcano after an eruption

• In layers of volcanic ash on the Earth’s surface

• Deep underground

• On the bottom of the ocean.

Mafic igneous rocks have a darker colour.

Some examples are:
Basalt, Gabbro, and Scoria

​​Mafic

Felsic igneous rocks have a lighter colour.

Some examples are:
Granite, Rhyolite, and Pumice

​​Felsic

Open Ended

Come up with a way to help remember what mafic and felsic mean.
Write it below.

For example:
Intrusive rocks form inside the Earth
Intrusive = Inside

Multiple Choice

Obsidian is known as volcanic glass due to its glassy appearance. Based on the image of obsidian, how would you classify this igneous rock?

• Mafic

• Felsic

• Intermediate

• Transparent

Multiple Choice

You are given 4 rock samples to observe, and make the following notes.

A - Dark and bumpy

B- Light and smooth

C- Dark and glassy

D- Light and bumpy

Which rock samples are most likely felsic rocks?

• A and C

• B and D

• A and D

• C only

As molten rock cools, the minerals from crystals.
The crystal size depends on how fast the molten rock cools.

​

Open Ended

A geologist wanted to investigate the relationship between molten rock cooling time and mineral crystal size.

Write a suitable hypothesis for this investigation.

Gabbro is an intrusive igneous rock, Basalt is an extrusive igneous rock. Use this information for the next question...

Multiple Choice

What is the relationship between cooling rate and crystal size?

• Faster cooling results in larger crystals.
• Cooling rate has no effect on crystal size.
• Slower cooling leads to smaller crystals.
• Slower cooling leads to larger crystals.

Multiple Choice

What other statement can be made about Gabbro and Basalt?

• Gabbro and Basalt are both felsic rocks.

• Gabbro and Basalt are both mafic rocks.

• Gabbro is a felsic rock, Basalt is a mafic rock.

• Gabbro is a mafic rock, Basalt is a felsic rock.