Metamorphic Textures

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Metamorphic Textures
Talc Tremolite Schist
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Two Main Categories

• Foliated
• A planar arrangement of textural features in a
  rock
• Rocks are categorized by their texture which
  reflects the amount of stress the rock has
  undergone
• Nonfoliated (Granular)
• Often monomineralic

Gneiss
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Foliated RocksLow Grade (Low-rank)
Low to moderate temperature and pressure
conditions

• Slate
• Fine grained
• Clays, micas, chlorite, graphite
• Slately cleavage (flat sheets)
• Protolith Shale

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Foliated RocksLow Grade

• Phyllite
• (Near) planar foliation
• Transitional between slate and schist
• Larger crystals than slate
• (but are usu not visible)
• Corrugated cleavage
• Phyllitc Sheen (High reflectance)
• Protolith Shale

Phyllite
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Foliated RocksMedium Grade

• Schist
• Schistosity (Distinct Fine Foliation)
• Common minerals (not limited to)
• Mica, chlorite, talc, graphite

Quartz Muscovite Schist
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Foliated RocksHigh Grade (High Rank)
High temperature and pressure conditions

• Gneiss
• Coarse grained
• Minerals separate into alternating monomineralic
  bands

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Nonfoliated RocksMonomineralic

• Quartzite
• Quartz
• Protolith Sandstone
• Medium grained
• Fractures through grains
• Marble
• Calcite
• Protolith Limestone
• Contact Metamorphism (High T)

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Nonfoliated RocksNot Monomineralic

• Hornfel
• Fine grained
• Brittle
• Lacks foliation
• Contact Metamorphism (High T)
• May contain high T minerals
• e.g. andalusite, cordierite

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Other Examples

• Mylonite
• Fine-grained rock formed by grinding during
  intense folding faulting
• Fiamme
• Lumps of flattened and stretched pumice and glass
  fragments that have become depressed into disk
  like forms.