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