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
Serpentine
Garnet
SillimaniteKyanite
Tourmaline
Staurolite
Metamorphic Processes1. 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 - FoliatedFoliated 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