Classification &
Identification of Metamorphic Rocks
Classification of Metamorphic Rocks is based primarily on texture, color
and kinds and proportions of minerals present. See Table 5.2.
To identify a metamorphic rock:
First identify the texture.
If it is foliated, use a name consistent with the foliation.
The name is then modified by dominant mineral names (if possible)
– quartz-biotite schist. Sometimes igneous names can be used
– granitic gneiss.
If a rock is non-foliated, it is named by mineral content
or recognition of relict textures:
Quartzite
Marble
Soapstone
Serpentinite (made of
serpentine)
Anthracite (hard coal, conchoidal fracture, vitreous luster)
Greenstone or greenschist
= low to medium grade metamorphosed basalt, andesite, gabbro.
Amphibolite = higher grade metamorphism of basalt, andesite,
gabbro.
Metaconglomerate, metagraywacke,
and metachert = metamorphic equivalents of these metamorphic rocks.
Hornfels: general name for contact metamorphosed
rocks that a re non-foliated and too fine grained for individual minerals
to be identified.