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Hornblende (Ca,Na)2-3(Fe,Mg,Al)5Si6(Si,Al)2O22(OH)2 Kaolinite (clay) Al2Si2O5(OH)4 Foliation ANIMATION 2
Grade Foliation type How does change as grade increases? Density increases (volume shrinks) Foliation increases Crystal size increases Why? Why? Grains and crystals pack closer together under confining pressure Minerals align when under directed pressure Grain boundaries migrate, enlarging crystal size as pressure (any kind) placed on crystal boundaries. to med Med to high Very high Rock or slaty cleavage Phyllitic Schistosity Gneissic Migmatitic 3
Grade Foliation Rock or slaty cleavage Microscopic, aligned mica minerals. Planar cleavage. No visible minerals. Dense. Grade to med Foliation Rock or slaty cleavage Phyllitic Microscopic, aligned mica minerals. Planar cleavage. No visible minerals. Dense. Mostly microscopic, aligned mica minerals. Only a few visible, isolated minerals peeking out of satiny background. Foliation is undulating. Grade to med Foliation Rock or slaty cleavage Phyllitic Microscopic, aligned mica minerals. Planar cleavage. No visible minerals. Dense. Mostly microscopic, aligned mica minerals. Only a few visible, isolated minerals peeking out of satiny background. Foliation is undulating. Med to high Schistosity Mostly visible biotite minerals all aligned, giving rock a scaly look, like a fish. Foliation is undulating and fine. Some large porphyroblasts may peek out. 4
Density separation during sand deposition (from hour glass) Grade Foliation type Gneissic All visible, interlocking crystals, separated into alternating dark- and light-colored layers. 5
Grade Foliation type Gneissic All visible, interlocking crystals, separated into alternating dark- and light-colored layers. Very high Migmatitic Gneissic where ½ melted, and the high temperatures caused folding of the layers. General mineral grade stability Medium -------------------------------------------------------------Quartz----------------------------------------------------------- -------------------------------------------------------------Feldspar--------------------------------------------------------- -------------------------------------------------------------Calcite------------------------------------------------------------ -------------------------------Muscovite---------------------------- ----------------------------Biotite------------------------------ ----------------------------Garnet------------------------------------------------- ---------------Hornblende----------------- ---------------Pyroxene----------------- 6
Metamorphic setting Contact metamorphism (C) Regional metamorphism: Deep burial (B) P : steadily increasing with depth T T : increasing toward magma : steadily increasing with depth Chemically Chemically active active fluids fluids from magma and from heated surface waters liberated from hydrous minerals and small amounts in cracks/pores Core Mountain Garnet from the Adirondack Mountains, NY Museum of Natural History, NY. Garnet-bearing amphibolite shows how metamorphism changes. Originally this rock was a GABBRO with olivine, pyroxene, and plagioclase. Under high T and P, water seeped into rock and reacted with original minerals to form hornblende and garnet. Water allowed for the large crystal size. Regional metamorphism: Converging continents (R) Subduction zone metamorphism (S) Hydrothermal (H) circulation at spreading centers : increasing with depth to liberated from medium: hydrous minerals and small increasing with amounts in cracks/pores depth : slowly from hydrous increasing with minerals in hydrothermally depth altered ocean crust and water trapped in pores/cracks because occurs at the Moho. from magmas and from circulating seawater 7
Sills Glacier National Park Basalt Sill, Glacier National Park, Montana 8
Eroding Metamorphic Rocks ANIMATION Review Display Samples Review Metamorphic Rock Chart Metamorphic Rocks Activity There are some duplicate names in the boxes. Metamorphic Rocks in North America Formulas You Need To Know CaCO 3 Mineral: Calcite Sedimentary rock: Chalk, Limestone Metamorphic (including rock: coquina, calcarenite) rock: Metamorphic rock: Marble SiO 2 Mineral: Quartz Sedimentary rock: Quartz Sandstone, Metamorphic Chert, Diatomite rock: rock: Metamorphic rock: Quartzite 9
Metamorphic settings B, R, S B, R, S S B, R, S B, R, S Parent rock GRADE: - Med Med - Very Shale Slate Phyllite Schist Gneiss Migmatite Granite Gneiss Migmatite Basalt Greenstone Blueschist Eclogite Chert (SiO 2 ) Quartzite (crystals grow larger) Limestone (CaCO 3 ) Marble (crystals grow larger) Metamorphic Metamorphic settings settings C C C C C H Parent rock GRADE: - Med Med - Very Chert (SiO 2 ) Quartzite (crystals grow larger) Limestone (CaCO 3 ) Marble (crystals grow larger) Mixture of minerals Skarn (crystals grow larger; form new minerals) Shale Hornfels Basalt Hornfels Mantle rock (Peridotite) Serpentinite Serpentinite Mt Diablo Soils derived from serpentine are toxic to many plants, because of high levels of nickel, chromium, and cobalt; growth of many plants is also inhibited by low levels of potassium and phosphorus and a low ratio of calcium/mag nesium. We have now completed this week s question sheet. On your own, review each question again. I recommend that you write out your answers (synthesize your thoughts and notes and put the answers into your own words). If something doesn t make sense or to just get some feedback, come see the tutors or me during my office hours. Remember: The exam will contain ANY question from ANY question sheet for this section. ROCK/MINERAL REVIEW 10