Download METAMORPHIC ROCKS CLASSIFICATION KEY FOLIATED ROCKS

METAMORPHIC ROCKS CLASSIFICATION KEY
FOLIATED ROCKS
“Protolith” = Parent Rock
ROCK NAME
GRAIN SIZE
SLATE
Fine-grained (too small
to see with the unaided
eye)
Foliation: thin, parallel layers; flat, nearly smooth surfaces; may look
as if it can easily be split into thin sheets.
Dull surface appearance
Typically has uniform color; comes in many different colors including
black, dark gray, green, brown, red
Fine-grained sedimentary
rocks (e.g. shale)
Fine-grained (grains
too small to see with
the unaided eye)
Foliation: thin, sometimes wavy layers; flat, nearly smooth surfaces;
may look as if it can easily be split into thin sheets.
Surface has a glossy sheen; colors similar to those of slate.
Shale; fine-grained
sandstone; slate
SCHIST
Medium-grained prominent mica
minerals, often contains
visible crystals
Foliation: layers highlighted by large, platy mica minerals
(muscovite, biotite, chlorite) in thin, parallel or wavy bands.
Surface is very shiny; may contain isolated crystals, commonly
garnet.
Sandstone; volcanic
igneous rock; any finegrained metamorphic rock
GNEISS
Coarse-grained crystals
Foliation: distinct crystals arranged in subparallel to parallel bands
of alternating light and dark colored minerals; appears striped.
Crystals may appear flattened or elongated parallel to foliation.
Plutonic igneous rock (e.g.
granite, diorite); coarsegrained clastic sedimentary
rocks; any fine-grained
metamorphic rock
PHYLLITE
CHARACTERISTICS
POSSIBLE PROTOLITH
NONFOLIATED ROCKS
ROCK NAME
GRAIN SIZE
MARBLE
Fine to coarse crystals
Composed of calcite or dolomite; reacts to HCl
Often has shiny or glassy luster; soft (may or may not scratch penny,
does not scratch glass); many colors, e.g. white, tan, pink, green.
Any type of limestone
QUARTZITE
Fine to coarse crystals
Composed mostly of quartz.
Glassy luster; may have crystalline or sugary appearance; hard (can
scratch glass); many colors, e.g. white, tan, pink, green.
Sandstone
Fine (not visible)
Black, shiny (almost glassy) appearance; looks similar to obsidian
but not as heavy or as dense
Coal
ANTHRACITE
COMPOSITION/CHARACTERISTICS
POSSIBLE PROTOLITH