Igneous rocks

Question 1

What is an igneous rock

Answer 1

A rock that has originated from a molten state such as lava from a volcano which then solidifies either externally (extrusive) or internally (intrusive)

Question 2

Intrusive

Answer 2

forms inside a volcano so therefore cools slower forming larger crystals

Question 3

Extrusive

Answer 3

forms outside of the volcano usually after an explosion, cools much quicker and therefore forms smaller crystals

Question 4

Silicates

Answer 4

crystalline rock structures forming igneous minerals based on a 203 dimensional array of silicon and oxygen held together by molecular bonds

Question 5

most common silicate

Answer 5

silica

Question 6

Where can silica be found (crystalline form)

Answer 6

usually in quartz

Question 7

What can pressure do to silica

Answer 7

At greater pressures silica minerals can form other minerals

Question 8

In what percentage of silica magma does quartz form in

Answer 8

more than 52%

Question 9

What is peridotite

Answer 9

Olivine and pyroxene

Question 10

What is present in high silica magma’s

Answer 10

Magnesium tends to be lower however, aluminium, calcium and sodium concentrations are higher - e.g. feldspars

Question 11

which minerals only form in water magma’s

Answer 11

mica and amphibole - occur in andesitic and granitic

Question 12

In lower silica magma’s, there is a higher concentration of ..1.. elements, especially ..2…

Answer 12

1. metallic

2. magnesium

Question 13

grain size definition

Answer 13

refers to the size of the particles involved in forming the rock- sedimentary rocks
igneous or metamorphic rocks- do not have particles, instead crystals so should arguably be crystal size for these rock types

Question 14

fractional crystallisation

Answer 14

minerals rich in iron or magnesium crystallise at higher temps whereas quartz and sodium- and potassium rich feldspars crystallise melt at lower temps

Question 15

Plutons

Answer 15

large igneous intrusion ranging in size from km3 to hundreds of km3 formed deep within the crust

Question 16

Batholith

Answer 16

large volume of material in the earths crust which can join plutons together

Question 17

Dyke

Answer 17

vertical fissures between the gabbro layer and basaltic pillow lavas. During sea floor spreading, successive dykes form a dyke only layer called a sheeted dyke layer

Question 18

Crystal (Rothery,2015)

Answer 18

Any substance which has a regularly repeating atomic structure

Question 19

silica percentage in basic and ultrabasic magmas

Answer 19

ultrabasic- less than 45%

basic- 45-52%