Instructor: Arthur Reed

Metamorphic Rock Classification

(Last update: March 8, 2015)

 

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TEXTURE

PARTICLE SIZE

COMPOSITION

COMMENT

ROCK TYPE

 

Non-foliated

Non-oriented grains

Medium to coarse grained, minerals visible

Calcite

(CaCO3)

Hardness of 3; fizzes with dilute HCL

Marble

Dolomite

(Ca,Mg)

(CO3)2

Fizzes with dilute HCL only when powdered

Dolomitic Marble

Quartz (SiO2)

H=7; breaks through grains (as opposed to sandstone that breaks around grains)

Quartzite

Amphibole; commonly hornblende

Generally black; prismatic crystals with 2 directions of cleavage at 60 / 120

Amphibolite

Anything that could be a conglomerate

Breaks through grains as well as around them; clasts may be flattened or stretched

Meta-conglomerate

Fine grained, minerals not visible

Clay minerals, mica

Dense, dark colored

Hornfels

Carbonaceous material

Black, shiny, conchoidal fracture

Anthracite Coal

 

 

TEXTURE

PARTICLE SIZE

COMPOSITION

COMMENT

ROCK TYPE

 

Foliated

Foliated

Fine grained, minerals not visible

Clay minerals, mica

Dense; thin pieces will pass the "tink" test

Slate

Clay minerals, mica

Satiny luster; very shiny and reflective in sunlight

Phyllite

Foliated or Lineated

Medium to coarse grained; size generally increases with metamorphic grade

Muscovite, biotite, chlorite, talc, garnet, kyanite, staurolite, feldspar, quartz, tourmaline, and many others

Name is preceded by diagnostic minerals: such as quartz schist, mica schist, quartz mica schist, kyanite biotite hornblende schist, etc.

Schist

Color Banded

Feldspar, quartz, mica, ferromagnesian minerals

Color banding due to alternation of light (felsic) and dark (mafic) minerals

Gneiss

Mixed metamorphic and igneous rock

Feldspar, quartz, mica, ferromagnesian minerals

Alternating layers of felsic igneous rock and mafic gneiss; the last metamorphic grade prior to complete melting

Migmatite

 

 

 

 


 

 

Mineral Change: clay chlorite quartz/feldspar/mica

 

Texture Change: bedding slaty cleavage schistosity mineral banding

 

Rock Change: shale slate phyllite schist gneiss

 

 

 

 

Based on information from the site of Mike Strickler, Rogue Community College