Lab 7
Metamorphic Rocks
Metamorphic Rocks
• Metamorphic rocks:
– rocks changed by T, P,
or action of watery hot
fluids
• Protolith:
– parent rock
– can be ign, sed, mm
Common minerals:
• Quartz, feldspars,
muscovite, biotite,
chlorite, garnet,
tourmaline, calcite,
dolomite,
serpentine, talc,
kyanite, sillimanite,
staurolite, and
amphibole
• Minerals help you
name the protolith
Garnet
Tourmaline
Serpentine
Kyanite
Sillimanite
Staurolite
Metamorphic Processes
1. Contact
metamorphism
• Occurs locally 
ign. intrusions
• If hydrothermal
fluids 
hydrothermal mm
• Low pressure
Metamorphic Processes
2. Regional
metamorphism:
• Occurs over large
regions  deep within
cores of rising
mountain ranges
• High stress & high
pressure
• Result from large ign.
intrusions that cool
over time
• May also have
hydrothermal alteration
Composition
• Mineral composition after metamorphism:
– Can stay the same
• Recrystallization – small minerals will convert to larger crystals
– Can change
• Neomorphism – minerals recrystallize and form different minerals
• Metasomatism – significant mineralogical change  chemicals are
added or lost and form different minerals
Textures - Foliated
Foliated texture – layering  parallel
alignment of platy minerals (micas) as a
result of applied pressure
– NOT depositional feature!
•
Slaty rock cleavage –more dense;
clanky
– Rock name: slate
•
Phyllite texture– wavy/wrinkled foliation;
shine
– Rock name: phyllite
•
Schistosity –visible platy minerals
and/or alignment of long prismatic
crystals; minerals visible; no comp
banding
– Rock name: schist
•
Gneissic banding – alternating layers;
minerals visible; comp banding
– Rock name: gneiss
Textures – Nonfoliated
• Nonfoliated texture – no
layering
– Crystalline texture – coarse
grained crystals
• Example: marble
– Microcrystalline texture – fine
grained crystals
• Example: hornfels
– Sandy texture – fused, sand-sized,
resembles sandstone
• Example: quartzite
– Glassy texture – homogenous
texture, no visible grains/structures
• Example: anthracite coal
Other Textures
• Stretched or sheared grains
• Porphyroblastic – large
crystal in ground mass (like
phenocryst)
• Hydrothermal veins –
fractures “healed” by ppt
from hydrothermal fluids
• Folds
• Lineations – lines on rocks:
foliations, shear planes,
slaty cleavage, or aligned
crystals.
Today’s Lab
• ID metamorphic rock samples (put rock #s
in order)
– May be more than one of the same thing
– Identify important mineralogy in name: i.e.,
kyanite schist
• Foliation demonstration
• Campus building stone exercise