Metamorphic Rocks (L9) Flashcards
What does metamorphism mean and involve
meta means change and morph means form so it involves a change in form, converting it from one rock type to another
What are the main agents of change?
heat, pressure, and chemically active fluids
What are the 3 main types of metamorphism?
contact metamorphism - involves heat, uniform pressure
regional metamorphism - involves heat, differential pressure
Metasomatism - involves reaction of minerals with active fluids during the process
When does contact metamorphism commonly occur?
when a pre-existing rock is heated by magma of an igneous intrusion, forming a metamorphic halo, or “aureloe” in the adjecent country rock
When does Regional Metamorphism commonly occur?
occurs when a pre-existing rock is heated (baked) under unequal pressure (differential stress)
in terms of texture, what are the main diff between contact and regional metamorphism?
the orientation of flat and platy or elongates minerals
In contact metamorphism, pressure is ____ and retains a ___
uniform (in all direction) and retains a random orientation
In which areas do regional metamorphism generally occur in?
areas where 2 lithospheric plates are pressing against one another, and rocks are subjected to differential stress (pressure applied unevenly)
How is foliation and bedding different?
foliation is a uniquely metamorphic characteristic, produced by the preferred alignment of platy/elongate minerals while bedding is a sedimentary characteristic
Rocks containing platy/elongate minerals that are subjected to regional metamorphism are ____
typically foliated
with increasing metamorphism, shale changes:
to slate, to phylite, to schist, and finally to gneiss
What is shale?
a sedimentary rock made of microscopic grains of clay and quartz
Why is shale called a parent rock?
because it is the rock we start off with
Shale’s property is?
very dull and breaks into layers
What do clay minerals from shale begin to transform into next and what is its foliation type called?
transforms into small, platy mica crystals that form slate
called Slaty Cleavage
The development of more distinct, sikly sheens due to further growth of platy mica crystals makes the rock ____
phylite and the foliation is phyllitic foliation
What rock is made from a medium to high metamorphic grade, and the appearance of obvious sparkles?
it is Schist and the foliation type is called schistose foliation
high t overy high metamorphyic grade, mica grains transform into more tabular, elongate crystals of amphibole or pyroxene. What rock is this and what is the foliation?
Gneiss and genissic foliation
What is the overall trend with icnreasing temp and differential pressure (metamorphic grade)?
foliation becomes more noticeable due to increse in degree of preferential alignment and size of platy/elongate grains
What is another way to recognize if a rock is metamorphic?
seeing if the rock is made of mineral crystals as opposed to particles
Foliated rocks such as slate and phylite are uesd for which purposes and why?
for architectural purposes b/c slate is durable and naturallly split into sheets of even thickness
Where is Gneiss used in?
similar decorative applications as granite, including countertops, headstones, and facing stone
Some metamorphic rocks, can have a non-foliated texture if it has undergone ___
contact metamorphism
Why are platy/elognate crystals randomly oriented?
because their growth wasn’t guided by uneven pressure
How can we distinguish calcite from quartz?
marble, being composed of calcite beraks in a way that tiny little cleavage planes shine in the light
Why are non-foliated metamorphic rock marble commonly used in sculptures?
b/c it is relatively soft, easy to carve, and has a relatively uniform texture
Why are limestones, which are made in the same composition, less desireable than marble?
because it tends to be weak along planes of bedding, so it can have the undesireable quality of spltting
When does metasomatism occur?
when fluids react with a pre-existing rock and alter the chemical composition of minerals within the rock
Serpentine
a rock formed y metasomatism and a hardness from 3-6
What happens if you add another step of fluid interaction to Serpentine and Quartz?
forms the mineral talc used in baby powder
Jade
another type of rock formed by metasomatism, extreme toughnesss, so can be carved into complex designs without breaking
