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Metamorphic Rocks
Rock Cycle
Objectives
14 – Describe the types of changes associated with metamorphic rocks.
15 – Contrast regional and contact metamorphism.
Metamorphic Rocks
Pre-existing rocks changed by heat and pressure
Different Types of Changes
Compaction Grains move closer. Rock becomes more dense. Porosity reduced. Example: clay to shale to slate
Recrystallization- Growth of new crystals. No changes in overall
chemistry. New crystals grow from the
minerals already present Foliation
Minerals separate into bands New minerals form from heat
and pressure
Types of Metamorphism: Contact Contact (thermal)
Small scale Associated with igneous
intrusions
Types: Regional Metamorphism Regional (dynamic)
Large scale Associated with mountain
building
Foliated vs. Non-foliated
Foliated – has bands or layers
Non-foliated - No banding Form from rocks made
up of single minerals
Rank
The degree of metamorphism required to change a rock
Quartzite
Non-foliated Visible minerals grains Low-high
metamorphisis Quartz Parent - Sandstone
Marble
Non-foliated Usually visible grains –
granular Will effervesce in HCl Calcite Parent - Limestone
Anthracite
Non-foliated Black color Metamorphosed Coal
Peat→Lignite→
Bituminous coal→ Anthracite
Slate
Foliated Small grain size Low metamorphism Visible layering A metamorphosed
shale
Phylite
Foliated Small-visible grains Low-medium
metamorphism Sheen Crenulations- slight
wavy appearance A metamorphosed slate
Schist
Foliatied Visible grain size Medium metamorphism Biotite, Garnet A metamorphosed
phylite Basalt may change into
schist
Gneiss
Foliated Large visible grains High degree of
metamorphism Definite banding and
recrystallization Horneblende, Quartz Metamorphosed schist