Lecture Fifteen

Question 1

Define a rock.

Answer 1

A coherent, naturally occurring solid, consisting of an aggregate of minerals or, less commonly, a mass of glass.
Coherent = sticks together, but can be broken into pieces.
Naturally occurring = not bricks or concrete etc.
Aggregate of minerals or mass of glass = most rocks are made of minerals, a few volcanic rocks are made of rapidly cooled glass.

Question 2

How do grains of minerals get together to make a rock?

Answer 2

Clastic rocks = Cemented with a natural glue - new minerals precipitate between grains making rock.
Crystalline rocks = Mineral grains lock and hold together like pieces of a jigsaw.

Question 3

What is bed rock?

Answer 3

Any rock that makes up the Earth surface.

Question 4

What is an outcrop?

Answer 4

Any rock at the Earth’s surface that you can interact with.

Question 5

What is a hand specimen?

Answer 5

Any rock or mineral small enough to easily hold in your hand.

Question 6

What are the three types of rocks? - Classified by how they are formed.

Answer 6

Igneous.
Sedimentary.
Metamorphic.

Question 7

What is igneous rock?

Answer 7

Formed when minerals crystallise out of a molten magma at or below the Earth’s surface.
All rocks start as Igneous, originally, but then they are affected by the Earths tectonic processes.

Once they are formed, they can be:
Remelted and recrystallised (igneous), eroded and redeposited (sedimentary) or buried and heated (metamorphic).

Question 8

What is sedimentary rock?

Answer 8

Formed from eroded and broken pieces of rocks at the Earth’s surface.
Form wherever sediments settle.
A piece of sediment that forms the rock is called a “clast” hence clastic rocks.

Once they are formed, they can be:
Eroded and redeposited (sedimentary), buried and heated (metamorphic) or melted and recrystallised (igneous).

Question 9

What are metamorphic rocks.

Answer 9

Any rock type that has been changed by heat, pressure, fluids or a combination of these things.
Formed when rocks get deeply buried, get lose to a magma chamber, or have hot fluids passed through them.

Once they are formed, they can be:
Melted and recrystallised (igneous), uplifted, eroded and deposited (sedimentary) or reburied and heated (metamorphic).