Earth Materials Test 1

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Author:
DrGirlfriend
ID:
261137
Filename:
Earth Materials Test 1
Updated:
2014-02-13 01:23:09
Tags:
Geology
Folders:
Geology 2005
Description:
Geology 2005 Test 1: Tectonic settings, crystal systems, mineral properties/optical mineralogy, rock melting and igneous rock classification
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  1. Divergent plate boundaries
    (rock types, locations, characteristics)
    • 1.) Igneous
    • - How: asthenosphere rises as plates separate
    • - Rocks: gabbro and basalt - partial melting of mantle = decompression melting of oceanic crust = mafic magma and lava

    • 2.) Sedimentary
    • - How: sediments accumulate farther away from ridge
    • - Rocks: Sandstone, shale

    • 3.) Metamorphic
    • - How: hot water from rising asthenosphere heats water = circulation = H2O gets into rocks = metamorphism
    • - Rocks: greenstones, amphibolites (low to medium grade metamorphic rocks of basalt)

    Examples: Mid-Oceanic Ridge, there's a rift valley in Iceland, East African Rift

    Continental rifts eventually lead to seafloor spreading (California Nevada, N.M./Colorado)

    Elevation is highest at ridge (hot rocks are buoyant)
  2. Convergent Plate boundaries
    • 1.) Igneous
    • - How: addition of H2O from subducting plate into asthenosphere = partial melting of mantle = basalt/gabbro
    • also, rising basalt from subducting oceanic crust = partial melting of oceanic arc crust = intermediate (diorite/andesite)

    • 2.) Sedimentary
    • How: sediments accumulate at subduction zone (as underlying plate goes down, rocks are scraped off and accumulate on overriding plate)

    • 3.) Metamorphic
    • - How: partial melting of mantle = contact metamorphism in subduction zone where magma chambers heat surrounding rock


    • Ocean-Ocean:
    • Example: The Caribbean, Aleutian Islands (off of Alaska), common around Pacific Ring of Fire
    • Island Arcs (chains of volcanoes) form above subduction zone

    • Ocean-Continent:
    • Example: Andes, Cascades
    • Volcanoes occur above subduction on overriding plate, Mountain-building = very high, more dense plate subducts

    • Continent-Continent
    • Example: Himalayas
    • Originally ocean-continent, then continent-continent and subduction stops
  3. Transform Plate Boundaries
    • Lithosphere is neither created nor destroyed
    • plates slide against each other

    Mostly metamorphic rocks strongly sheared fabrics

    Example: San Andreas Fault in California
  4. Grain Size Classification Igneous Rocks
    • 1.) Aphanitic
    • cools fast
    • crystals too small to be seen by eyes

    • 2.) Phaneritic
    • cools slowly
    • can see crystal with naked eyes

    • 3.) Porphyritic
    • slow and fast cooling
    • --> magma slowly cools, then suddenly rises and cools quickly
    • bimodal grain size (coarse and fine-grained)
  5. Igneous Rock Textures
    • Pegmatitic
    • very large crystals
    • forms veins/layers within plutonic rocks

    • Pyroclastic/Fragmental/Welded
    • disaggregated igneous material (erupted at surface, disaggregated, quickly deposited from air/water, formed rock)

    • Vesicular
    • pores
    • gases present magma
    • highly explosive due to dramatic as magma moves to surface

    • Glassy
    • no crystals (obsidian)
  6. How rocks melt
    • 1.) Add volatiles (like H2O)
    • - subduction zones
    • - adding water moves the solidus line

    • 2.) Increase Temperature
    • - hot spots, magmatic arcs
    • - raise T = atoms vibrate more = break bonds

    • 3.) Decrease Pressure
    • - divergent boundaries (mid-ocean ridge)
    • - P holds lattice of atoms together --> decrease P = lattice no longer rigid
    • - inner core (solid, high P) vs. outer core (liquid, low P)
  7. Two ways to classify the Earth's layers
    • 1.) Composition
    • - Crust
    •     >Oceanic = mafic, dense, younger, gabbro and basalts
    •      >Continental = felsic/intermediate, less dense, older, granite/rhyolite/andesite/diorite and some basalts
    • - Mantle
    •      >solid that can flow
    •      >higher T and P
    • - Core
    •      >iron and nickel
    •      >Outer = liquid
    •      >Inner = solid (high P)


    • 2.) Mechanical Behavior
    • - Lithosphere
    •      >solid part of upper mantle and crust
    •      >brittle behavior
    • - Asthenosphere
    •      >the rest, I guess
    •      >ductile behavior
  8. How minerals form
    - crystallize from magma

    - growth from solid-state reactions

    - precipitate
  9. What is a mineral (by definition)
    • 1.) Naturally occurring solid (not man-made, not a liquid or gas)
    •      >window glass not a mineral, but volcanic glass is
    •      >liquid water not a mineral, but water ice is

    • 2.) Inorganic (not alive at any point in time)
    •      >calcite = exception (formed from shells)

    • 3.) Ordered internal crystalline structure
    •      >with repeatable unit cell

    • 4.) Definite chemical composition
    •      >can be expressed as a formula
  10. What is a rock?
    a naturally occurring solid composed of one or more minerals
  11. What are minerals made of?
    Elements! duh
  12. Most common elements in Earth's crust (8 Major Elements)
    1.) Oxygen (46%)

    2.) Silicon (28%)

    3.) Aluminum (8%)

    4.) Iron (6%)

    5.) Magnesium (4%)

    6.) Calcium (2.4%)

    7.) Potassium (2.3%)

    8.) Sodium (2.1%)
  13. Atomic Radii, Ionic Radii
    - Atomic Radius decreases going left on Periodic Table

    - Ionic Radii smaller than neutral radius
  14. Physical properties of minerals
    Good ones for identifying minerals: habit, streak, hardness, cleavage, opacity/luster, specific gravity

    Not so good: color (think quartz)


    Habit - external shape/appearance (determined by how a mineral grows)

    Hardness - harder mineral can scratch softer ones, ranked relatively by Mohs Hardness Scale

    Density (specific gravity) - ratio of

    • Tenacity - how a mineral responds to short-term stress
    •      >flexible, brittle, malleable

    • Form of growth surfaces
    •      >euhedral, subhedral, anhedral

    • Cleavage - tendancy to break along flat planes
    •      >breaks along weak bonds

    Striations - furrows in rock due to fault movement (in plag = due to twinning)

    • Opacity - degree to which mineral transmits light
    • Luster - how mineral reflects light (metallic or nonmetallic)

    Streak - color of mineral in powder form
  15. Silicate Mineral Groups
    • 1.) Nesosilicates
    • - isolated SiO4 tetrahedra
    • - olivine, garnet, zircon
    • - WEAK

    • 2.) Sorosilicates
    • - pairs of linked tetrahedra
    • - epidote most common (LOW GRADE METAMORPHIC ROCKS)
    • - look for 2:1 ratio of Si to O

    • 3.)Cyclosilicates
    • - "ring silicates"
    • - beryl

    • 4.) Inosilicates
    • - chains
    •      >Single: ratio of Si to O is 1:3, pyroxenes
    •      >Double: chains linked thru shared O atoms, 4:11, Amphibole
    • - CLEAVAGE 120/60

    • 5.) Phyllosilicates
    • - sheets/planar arrangements
    •      >muscovite, mica, clay minerals
    •      >FINE-GRAINED, SINGLE PLANE CLEAVAGE, intermediate to felsic

    • 6.) Frameworks/Tectosilicates
    • - 3D interlocking network of tetrahedra (link through O atoms), 1:2
    • - quartz --> strong, lots of polymorphs
    • - feldspars
    • - resistant to weathering
    • - conchoidal fracturing
  16. Polymorphs
    • minerals with the same chemical structure, but different compositions
    • - form at different temperatures and pressures

    Calcium Carbonate: calcite/aragonite

    Olivine, Wadsleyite, Ringwoodite
  17. Optical properties of minerals
    • 1.) Color
    • - noly in PPL
    • - changes with light type/intensity

    • 2.) Pleochroism
    • - different absorbed differently by different crystallographic directions
    • - rotate stage to observe

    • 3.) Releif
    • - measures relative difference in index of refraction
    • - Hi Relief = more intense

    • 4.) Birefringence
    • - colors seen in xpl
    • - interference colors
    • - cleavage can be observed
  18. Isotropic vs. anisotropic
    • Isotropic - black in all orientations
    • - like garnet

    Anisotropic - capable of reorienting light

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