Metamorphic Rocks

 MiraCosta Collete

Metamorphic rocks are classified in a variety of ways:

1. by mineralogical composition (related to metamorphic facies (degrees of metamorphism intensity related to exposure to heat, pressure).
2. by protolith (if the original rock can be determined before it was altered to its current form).
3. by unique characteristics (crystalline texture, cleavage, layering, and structures).

Note there are a variety of metamorphic rock classifications that are much more technical than the simplified version presented here.

Click on images for a larger view.
a flat, thinly layered gray rock, lacks crystals
Slate 29		 A beach cobble composed entirely of fine crystalline quartz and displays percussion marks on its surface.
Quartzite 16		 a rock with layered bands of red and light gray quartzite displayed with a U-shaped fold.
Quartzite (folded) 17		 A dense gray and white finely crystalline rock display layered bands of pink and dark gray.
Metasandstone 15		 a trightly cemented conglomerate cobble compose of some crushed pebbles of quartz, chert, and dark rock fragments.
Metaconglomerate 14
A black and white striped crystalline rock with crystal oriented along layers.
Gneiss 6		 A gray and white banded crystalline rock with tightly crenulated folding
Gneiss crenulated 4		 A gray and white stryped crystalline rock displaying a tight v-shaped fold.
Gneiss schist 5 		A sample of shiney muscavite in a layered crystalline schist.
Schist 19		 a finely laminated micaceous (mostly biotite) schist.
Schist 20
Foliated schist
Schist 35		 a shiny green, flakey rock mad mostly of the mineral chlorite
Greenschist 8		 a stream cobble showing green, bluish gray, and white thin crystal banding
Greenschist blueschist 7		 a blueisgray rock with light-colored crenulated striation.
Blueschist 1		 A dark, crystalline rock composed mostly of fiberous-appearing layered crystals of hornblende with some white speckles of feldspar.
Amphibolite Schist 28
a minely crystaline white marble with green tremolite crystal formed in a radiating pattern.
Marble 10		 A white rock composed of large calcite crystals.
Marble 11		 A white finely crystalline rock with gray-striped banding.
Dolostone marble 2
Marble dolostone 33		 A brown, altered piece of vescicular basalt with a thick veien of mixed layers of calcite and quartz cutting across it
Calci-silicate rock 30
Foliated layers of green-banded metachert.
Metachert 32		 A complexly fractured and healed green and white chert with fractures fill with black chert
Metachert breccia 24		 a red smooth jasper cut by multiple small fracture of gray chert.
Metachert jasper 12		 a mostly red jasper with amix of other colors in irregular patterns.
Metachert 13		 Greenstone cobble with a quartz vein cutting through.
Greenstone 31
a fine to medium crystaline rock composed of the green mineral enstatite
Greenstone scarn 8		 A smooth, shiney or scaly mostly green piece of serpentinite, tapered on both ends like a watermelon seed.
Serpentinite (facoid) 22		 A smooth, shiney or scaly mostly blue piece of serpentinite
Serpentinite (blueshist) 21		 A smooth, shiney or scaly, naturally polished, mostly blue piece of serpentinite, tapered on both ends like a watermelon seed.
Serpentinite (facoid) 26 		A weathered brown, green, and black, coarsely crystalline rock with a white natrolite vein cutting through it.
Harzburgite 27
A block of crystalline rock display tight fold in dark schist and gneist cut diagonally by a white aplite-filled fracture.
Migmatite 25		 a gray granitic crystalline rock with large pyrope garnet crystals
Granulite 3		 Eclogite - blue-schist.
Eclogite 34		 A complexly shattered and welded sample green schist
Schist (fault gauge) 18 		A brown rock with a white surface that shows striations and chatter marks created by fault displacement.
Slickensides 23
See Introduction to Physical Geology: Chapter 10 - Metamporphism and Metamorphic Rocks More rocks may be added as they become available.
https://gotbooks.miracosta.edu/rocks/metamorphic_rocks.html 5/2/2022