Instructor: Arthur Reed

Metamorphic Rock Classification

(Last update: March 8, 2015)

Start Here	TEXTURE	PARTICLE SIZE	COMPOSITION	COMMENT	ROCK TYPE
Non-foliated â	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 â	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 è chlorite è quartz/feldspar/mica

Texture Change: bedding è slaty cleavage è schistosity è mineral banding

Rock Change: shale è slate è phyllite è schist è gneiss

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