Metamorphic Rocks

Question 1

Describe slate

Answer 1

Low grade metamorphic rock
Slaty cleavage
Fine grained clay minerals
Dull lustre
Foliated
Minerals include Muscovite and chlorite
Protolith is shale

Question 2

Describe phyllite

Answer 2

Fine grained
Schistosity
Silky/crenulated appearance
Minerals include chlorite, Muscovite and biotite
Foliated
Protolith = shale or slate

Question 3

Describe Schist

Answer 3

Medium to course grained
Planar foliation/schiscosity
Shiny lustre
Foliated
Minerals include Muscovite, biotite,feldspar, quartz, garnet, staurolite and kyanite
Protolith = shale/slate/phyolite

Question 4

Describe gneiss

Answer 4

High grade Distinct mineral banding (light and dark layers)
Foliated and crystalline
Minerals include feldspar, quartz, biotite, hornblende, pyroxene, sillimanite
Protolith is shale or granite

Question 5

Describe Amphibolite

Answer 5

Low grade
Medium to course grained
May be weakly Foliated or have a flaky aprearance
Not Foliated
Minerals include hornblende, plagioclase feldspar and garnet
Protolith = Basalt

Question 6

Describe Hornfels

Answer 6

Fine grained
Forms form contact metamorphism
Low grade
Not Foliated and granular

Question 7

Describe Marble

Answer 7

High grade
Medium grained
Interlocking crystals
Minerals include calcite, clay minerals, quartz and micas
Not Foliated, crystalline and granular
Protolith = limestone

Question 8

Describe quartzite

Answer 8

Fractures cut through not around sand grains
From the fusion of quartz crystals
Minerals include Quartz
Not Foliated, crystalline, granular
Protolith = sandstone

Question 9

Describe anthracite

Answer 9

Coal
Very fine grained
Black
Brilliant lustre
Conchoidal fracture
Minerals include carbon
Not Foliated
Protolith = bituminous coal

Question 10

Describe Granulite

Answer 10

Medium to course grained
High grade
Minerals include pyroxene, anorthite, quartz, garnet
Not Foliated And granular
Protolith = basalt

Question 11

Greenschist

Answer 11

Dehydration reaction of mafic minerals
Low grade
Minerals include chlorite, actinolite, albite, epidote
Foliated
Protolith = basalt or Gabro

Question 12

What is schiscocity

Answer 12

Type of foliation with Parallel alignment of platy minerals due to high temps and pressures perpendicular to direction of maximum stress
In Intermediate grade metamorphic rocks which have undergone complete recrystallisation

Question 13

What is slaty cleavage

Answer 13

Parallel foliation of fine grained platy minerals perpendicular to direction of maximum stress
In fine grained low grade metamorphic rocks

Question 14

Metamorphic grade of gneiss at each stage

Answer 14

Shale > slate > phyllite > schist > gneiss > magmatite
Sedimentary > low > low to intermediate > intermediate > high > high

Question 15

define metamorphism

Answer 15

when a previous existing rock is subject to prolonged temperatures and pressures different to those under which they formed causing physical and chemical changes.

Question 16

define diagnesis

Answer 16

changes to sedimentary rocks due to heat and pressure. stage before metamorphism

Question 17

dehydration reaction

Answer 17

when hydrous minerals such as clays and micas become unstable they expelled water as they recrystallise, creating anhydrous (no water) minerals.

Question 18

decarbonation reaction

Answer 18

when carbon dioxide is expelled from minerals due to recrystallisation

Question 19

what factors effect the metamorphic rock that forms?

Answer 19

chemical composition of parent rock
minerals present
temperatures and pressures reached
time exposed to temperature and pressures
presence of hydrothermal fluids

Question 20

load pressure

Answer 20

uniform pressure which acts equally in all directions.
doesn’t alter grain shape

Question 21

directional pressure

Answer 21

when more force is applied in one direction which flattens the grains

Question 22

contact metamorphism

Answer 22

heat from igneous intrusion or other source. zone of metamorphism is called the metamorphic aureole

Question 23

regional metamorphism

Answer 23

heat and pressure from burial and tectonic movement over long periods of time. often over extensive areas. foliation prominent.
eg gneiss

Question 24

types of foliation

Answer 24

slaty cleavage
schistosicy
gneissic texture

Question 25

dynamic metamorphism

Answer 25

from high directional pressures and frictional heating alone fault and thrust zones. can produce mylonite texture near faults deep below the earths surface.

Question 26

metasomatism

Answer 26

when hydrothermal fluids which cary dissolved minerals percolate through rocks and react with minerals present and chemically alter/change them. minerals may be completely replaced by new ones.

Question 27

what causes folding

Answer 27

when high directional pressures and temperatures are applied to rocks over long periods so they act as plastic solids allowing them to fold without fracturing

Question 28

list the index minerals from low to high grade

Answer 28

chlorite, biotite, garnet, staurolite, kyanite, sillimanite