CLASSIFICATION OF METAMORPHIC ROCK SPECIES

MINERAL COMPOSITION OF ROCK	TEXTURE OF ROCK	GRAIN SIZE	SPECIES NAME
Clays, mica family minerals	Schistose*	Microscopic, not visible even with hand lens	SLATE
Clays, Mica family minerals	Schistose	Fine-grained, some visible with hand lens	PHYLLITE
Mica family minerals, quartz, garnet**	Schistose	Medium-grained to slightly coarse	SCHIST
Quartz, micas, feldspars, amphiboles, and pyroxenes	Foliated	Coarse, light and dark interlayered bands	GNEISS
Amphiboles, usually hornblende, and plagioclase feldspar	Foliated	Coarse, banded	BANDED AMPHIBOLITE
Quartz	Homogenous	Fine to medium	QUARTZITE
Calcite	Varies	Microscopic to medium	MARBLE
Amphibole, usually hornblende, and plagioclase feldspar	Non-foliated	Fine to medium	AMPHIBOLITE
Rounded rock fragments in groundmass	Non-foliated	Coarse	METACONGLOMERATE
*Schistose refers to the property of the rock displaying subparallel orientation of the micaceous and platy mineral grains. The rock SCHIST best displays the property of schistose texture.
**May also contain varying amounts of staurolite, kyanite, sillimanite, and andalusite.

It should be noted that some rocks may have been metamorphosed and NOT fit neatly into the above classification scheme. These are often generally referred to as metasediments, the prefix "meta" designating metamorphic origin.

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GENERALIZED RESULTS OF THE METAMORPHIC PROCESS

ORIGINAL ROCK	METAMORPHIC ROCKS -----------------------------------------------> Increasing Metamorphism
Shale	------>	Slate	------>	Phyllite	------>	Schist	---->	Gneiss
Rhyolite	------------------------------------------------------------------->							Gneiss
Granite	------------------------------------------------------------------->							Gneiss
Basalt	------------------------------------------------->					Schist	---->	Gneiss
Limestone	--------------------------->			Marble
Sandstone	--------------------------->			Quartzite

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Last updated on October 6, 2005

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