2.2

Question 1

What is assimilation?

Answer 1

This is the gradual melting of a Xenolith into magma.

Question 2

What is a Xenolith?

Answer 2

A foreign rock that has broken off and fallen into magma that is intruding the country rock.

Question 3

What is an igneous rock?

Answer 3

A rock that has cooled from magma.

Question 4

What is magma?

Answer 4

Molten rock.

Question 5

What is lava?

Answer 5

Molten rock that has cooled at the surface.

Question 6

What is a silicic igneous rock?

Answer 6

An igneous rock with a composition rich in silica, of more than 66% and are light coloured.

Question 7

What is an ultramafic igneous rock?

Answer 7

They have a silica content of less then 45% and are dark.

Question 8

What are felsic minerals?

Answer 8

They are silica rich and light coloured.

Question 9

What rocks make up about 95% of the earth crust?

Answer 9

Igneous.

Question 10

What is the name for a very large crystal?

Answer 10

A phenocryst.

Question 11

What is the texture of a rock if no crystals can be seen, even with a hand lens?

Answer 11

The rock is said that have a glassy texture.

Question 12

What crystals are formed when the rock has cooled quickly?

Answer 12

Fine grained crystals. Less than 1mm in size. Individual crystals cannot be seen.

Question 13

What crystals are formed when the rock cools slowly?

Answer 13

Coarse grained crystals. 1-5mm in size and can be identified by eye.

Question 14

Name the 2 felsic minerals.

Answer 14

Feldspar and Quartz. Which are both rich in silica.

Question 15

What is the most common rock forming mineral?

Answer 15

Feldspar.

Question 16

How would you recognise feldspar in an igneous rock?

Answer 16

Potassium feldspar:
•Usually has a pink colour.
Plagioclase feldspar: 
•Has a grey or white colour.
Both types of feldspar:
•Can be scratched with a steel nail
•Have a glassy appearance when looked at through a hand lens.