Metamorphic Rocks

Key info on the texture and structure of metamorphic rocks

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Metamorphic Rocks

Size

Regional

Coarse - Gneiss

Medium - Schist

Fine - Slate

All formed from regional metamorphism of mudstones and shales.

Contact

Marbles and metaquartzites become coarser the closer they are to the intrusion.

Mudstones/shales

hot = hornfels

warm = spotted slate.

Porphyroblastic

Large crystals e.g. Garnet surounded by finer crystals e.g. micas in a Garnet Mica Schist

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Shape

12 sided/Rhombic faced

Garnets can be well formed

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Orientation

Random in contact metamorphisim

Foliated in regional metamorphism

High Grade foliation = Gneissose Banding

Medium Grade Foliation = Schistosity

Low Grade Foliation = Slatey Cleavage

Preferred orientation

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Texture

Texture =

SIZE

SHAPE

ORIENTATION

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