3. Metamorphic Classification

3. Metamorphic Classification - Metamorphic rocks are...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Metamorphic rocks are classified on the basis of Metamorphic rocks are classified on the basis of texture texture and and composition composition (either mineralogical or (either mineralogical or chemical) chemical) Classification of Metamorphic Rocks Unlike igneous rocks, which have been plagued by a proliferation of local and specific names, metamorphic rock names are surprisingly simple (e.g. schist, gneiss) Addition of prefix modifiers provide flexibility if an important or unusual textural or mineralogical aspect needs to be stressed (e.g. mica schist, granite gneiss) Basic textural subdivision of metamorphic Basic textural subdivision of metamorphic rocks is into rocks is into foliated foliated and and non-foliated non-foliated types types Classification of Metamorphic Rocks Foliation: any planar fabric element Lineation: any linear fabric element These terms have no genetic connotations Some high-strain rocks (e.g. mylonites) may be foliated, but are treated separately Traditionally, the property of a rock to split along a Traditionally, the property of a rock to split along a regular set of sub-parallel, closely-spaced planes regular set of sub-parallel, closely-spaced planes A more general concept adopted by some geologists is to A more general concept adopted by some geologists is to consider cleavage to be any type of foliation in which the consider cleavage to be any type of foliation in which the aligned platy phyllosilicates (chlorite and mica) are too aligned platy phyllosilicates (chlorite and mica) are too fine grained to see individually with the unaided eye fine grained to see individually with the unaided eye Metamorphic rock with cleavage is a Metamorphic rock with cleavage is a SLATE SLATE or, if the or, if the platy phyllosilicates are just large enough to be seen, a platy phyllosilicates are just large enough to be seen, a PHYLLITE PHYLLITE Foliated Metamorphic Rocks Types of Foliation Types of Foliation 1. Cleavage: 1. Cleavage: Slate Slate Phyllite Foliated Metamorphic Rocks Types of Foliation Types of Foliation 2. Schistosity: 2. Schistosity: A preferred orientation of inequaint mineral grains or A preferred orientation of inequaint mineral grains or grain aggregates produced by metamorphic processes grain aggregates produced by metamorphic processes Aligned minerals are coarse grained enough to see with the unaided eye The orientation is generally planar, but linear orientations are not excluded Metamorphic rock with a schistosity is a SCHIST Biotite schist Garnet-mica schist Gneissose rocks are generally coarse grained Gneissose rocks are generally coarse grained Foliated Metamorphic Rocks Types of Foliation Types of Foliation Either a poorly-developed schistosity or segregated into layers by metamorphic processes 2. Gneissic Banding: 2. Gneissic Banding: A metamorphic rock with gneissic banding is a GNEISS Banding usually not a mechanical plane of weakness Biotite Gneiss Biotite Gneiss Foliated Metamorphic Rocks...
View Full Document

Page1 / 21

3. Metamorphic Classification - Metamorphic rocks are...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online