Lab 7 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 Sillimanite Kyanite Tourmaline 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