Metamorphic Rocks Flashcards
Describe slate
Low grade metamorphic rock
Slaty cleavage
Fine grained clay minerals
Dull lustre
Foliated
Minerals include Muscovite and chlorite
Protolith is shale
Describe phyllite
Fine grained
Schistosity
Silky/crenulated appearance
Minerals include chlorite, Muscovite and biotite
Foliated
Protolith = shale or slate
Describe Schist
Medium to course grained
Planar foliation/schiscosity
Shiny lustre
Foliated
Minerals include Muscovite, biotite,feldspar, quartz, garnet, staurolite and kyanite
Protolith = shale/slate/phyolite
Describe gneiss
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
Describe Amphibolite
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
Describe Hornfels
Fine grained
Forms form contact metamorphism
Low grade
Not Foliated and granular
Describe Marble
High grade
Medium grained
Interlocking crystals
Minerals include calcite, clay minerals, quartz and micas
Not Foliated, crystalline and granular
Protolith = limestone
Describe quartzite
Fractures cut through not around sand grains
From the fusion of quartz crystals
Minerals include Quartz
Not Foliated, crystalline, granular
Protolith = sandstone
Describe anthracite
Coal
Very fine grained
Black
Brilliant lustre
Conchoidal fracture
Minerals include carbon
Not Foliated
Protolith = bituminous coal
Describe Granulite
Medium to course grained
High grade
Minerals include pyroxene, anorthite, quartz, garnet
Not Foliated And granular
Protolith = basalt
Greenschist
Dehydration reaction of mafic minerals
Low grade
Minerals include chlorite, actinolite, albite, epidote
Foliated
Protolith = basalt or Gabro
What is schiscocity
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
What is slaty cleavage
Parallel foliation of fine grained platy minerals perpendicular to direction of maximum stress
In fine grained low grade metamorphic rocks
Metamorphic grade of gneiss at each stage
Shale > slate > phyllite > schist > gneiss > magmatite
Sedimentary > low > low to intermediate > intermediate > high > high
define metamorphism
when a previous existing rock is subject to prolonged temperatures and pressures different to those under which they formed causing physical and chemical changes.
define diagnesis
changes to sedimentary rocks due to heat and pressure. stage before metamorphism
dehydration reaction
when hydrous minerals such as clays and micas become unstable they expelled water as they recrystallise, creating anhydrous (no water) minerals.
decarbonation reaction
when carbon dioxide is expelled from minerals due to recrystallisation
what factors effect the metamorphic rock that forms?
chemical composition of parent rock
minerals present
temperatures and pressures reached
time exposed to temperature and pressures
presence of hydrothermal fluids
load pressure
uniform pressure which acts equally in all directions.
doesn’t alter grain shape
directional pressure
when more force is applied in one direction which flattens the grains
contact metamorphism
heat from igneous intrusion or other source. zone of metamorphism is called the metamorphic aureole
regional metamorphism
heat and pressure from burial and tectonic movement over long periods of time. often over extensive areas. foliation prominent.
eg gneiss
types of foliation
slaty cleavage
schistosicy
gneissic texture
dynamic metamorphism
from high directional pressures and frictional heating alone fault and thrust zones. can produce mylonite texture near faults deep below the earths surface.
metasomatism
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.
what causes folding
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
list the index minerals from low to high grade
chlorite, biotite, garnet, staurolite, kyanite, sillimanite
