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Metamorphic Rocks Cheat Sheet (DRAFT) by

GEOS100 - metamorphic rocks cheat sheet

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Metamo­rphic Textures

Formed under high heat and low pressure and have an interl­ocking grain appearance like marble
Formed under earth's interior under high pressure and high heat in directed pressure, causing a banded appearance like schist

Types of Metamo­rphism

Contact metamo­rphism
Produces an aureole around an intrusive body and occurs when rock is heated by an igneous intrusion. Results in non-fo­liated textures eg, limestone to marble.
Regional metamo­rphism
Produces most metamo­rphic rocks which are usually very foliated, from areas that have undergone change in physical conditions like temp, pressure, and stress. eg, shale to slate
  Regional metamo­rphism of basalt
 ­  Metamo­rphic rocks derived from basalt have more
 ­  minerals containing iron and magnesium than slate
 ­  and the foliation is less pronou­nced.
 ­  Greens­chist - low grade; ferrom­agn­esian mineral are
 ­  hydrated to form chlorite.
 ­  Amphib­olite - higher grade than greens­chist; chlorite
 ­  & other minerals lose water and convert to amphibole.
 ­  Granulite - high grade; amphiboles are further
 ­  dehydrated to produce pyroxene and garnets; little
 ­  orient­ation of the minerals
Subduction zone metamo­rphism
Special conditions of high pressure and low temp; rock exhibits foliation and is called bluesc­hist; higher grade rock is called eclogite
Aureole - an area that surrounds metamo­rphized rock due to being in contact with an igneous intrusion


Changes that happen when a rock is subjected to temps/­pre­ssures higher than where they formed.
Protolith can be any type of rock.
Recrys­tal­liz­ation in the solid state
Change in texture and mineralogy of the rock due to the new enviro­nment
Protolith - Parent rock

Metamo­rphic Grade

Metamo­rphic grade
reflects the intens­ity­/grade of metamo­rphism and is indicated by the sequential appearance of index minerals and by textures.
Common index minerals in ascending order of P/T: chlorite, muscovite (mica), biotite (mica), garnet, stauro­lite.
quartz and feldspar are always stable.
Burial metamo­rphism is the mild alteration of rock that occurs in deep sedime­ntary basins and ocean trenches
Index minerals - a mineral that forms under specific pressure and temper­ature to provide metamo­rphic history.

Contro­lling Factors in Metamo­rphism

Heat: most important agent of metamo­rphism
Influences the mobility and reactivity of chemically active fluids and is the result of intrusive igneous bodies or earths internal heat
Compos­ition of protolith
Chemical compos­ition is inherited from the parent rock
Changes the physical charac­ter­istics of rocks
  Confining pressure applies forces equally in all directions and causes harder and denser metamo­rphic rocks
  Directed pressure applies unequal pressure in different directions and causes distortion
Chemically active fluids present
At depth, higher temps and pressures cause minerals to dehydrate. Ions are expelled with the water and can travel to cause recrys­tal­liz­ation