Metamorphic rocks
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Metamorphic Rocks. “If something is gneiss, don’t take it for granite.”. Metamorphic Agents. Pressure (>1,000 times atmospheric pressure) Temperature (>300 degrees C) Chemical Fluids (mineral saturated hot water). Metamorphic Environments. Contact (thermal) – intrusion by magma

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Metamorphic Rocks

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Metamorphic rocks

Metamorphic Rocks

“If something is gneiss, don’t take it for granite.”


Metamorphic agents

Metamorphic Agents

  • Pressure (>1,000 times atmospheric pressure)

  • Temperature (>300 degrees C)

  • Chemical Fluids (mineral saturated hot water)


Metamorphic environments

Metamorphic Environments

  • Contact (thermal) – intrusion by magma

  • Hydrothermal – ion-rich hot water circulates through cracks

  • Mountain Building – regional metamorphism


Metamorphic changes rocks adjust to new conditions by

Metamorphic Changes -Rocks adjust to new conditions by:

  • Changes in texture

  • Changes in mineralogy


Changes in texture

Changes in Texture

  • Compaction

  • Recrystallization - may cause

    • Foliation

    • Lineation


Changes in minerology

Changes in Minerology

  • Recrystallization – small crystals reform into larger crystals of the same mineral

  • Formation of new minerals – elements recombine to form new minerals

    • Garnet, Chlorite and others found only (or mostly) in metamorphic rock


Grades of metamorphosis

Grades of Metamorphosis

  • Low Grade – Low temperature and pressure results in slate and phyllite

    • “Rock cleavage” in slate

    • Foliated

    • Fine grained

    • Slate looks dull, phyllite is shiny


Grades of metamorphosis cont

Grades of Metamorphosis (cont.)

  • Intermediate Grade – higher temperatures and pressures than Low Grade

    • Schist

      • Foliated

      • Mica, garnet


Grades of metamorphosis cont1

Grades of Metamorphosis (cont.)

  • High temperatures and pressures

    • Gneiss and Migmatite

      • Dark & light banding of mica (dark), quartz & feldspar (light)


Foliated metamorphic rock sequence

Slate – parent rock is shale (sedimentary)

Phyllite – parent rock is slate

Schist – parent rock is phyllite

Gneiss – parent rock is schist

Migmatite – parent rock is gneiss

Foliated Metamorphic Rock Sequence


Non foliated metamorphic rocks their parent rocks

Non-Foliated Metamorphic Rocks & Their Parent Rocks

  • Marble – Parent rock is limestone or dolostone (calcite, reacts with acid)

  • Quartzite – Parent rock is sandstone

  • Anthacite – Parent rock is bituminous coal

  • Hornfels – Parent rock is any rock type


Metamorphic rock dichotomous key

Metamorphic Rock Dichotomous Key

Proceed to Dichotomous Key Activity


Metamorphic rocks

View in slide show, then click to view:

Dichotomous Metamorphic Key


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