Geology Midterm Review

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Accretion

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(the planets formed through accretion)after formation of solar system from solar nebula, dust grains clump together, then clumps collide and stick together forming bodies several km in diameter…these bodies collide forming 'proto-planets'

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Rock

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aggregate of one or more minerals

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Mineral

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a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal structure and physical properties
[Note: Some minerals exhibit range of chemical compositions: i.e.: olivine]

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Ionic and Covalent bonding

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Ionicinvolves one atom donating one or more electrons to another atom that accepts them
Covalentinvolves the sharing of electrons between two atoms

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Crystalline

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solid with regular and repeated arrangement of atoms throughout the crystal structure

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Unit cell

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the small basic building block

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Plane lattice

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how the unit cells are arranged in 2-D

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Space lattice

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how the plane lattices are arranged in 3-D

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Types of Unit Cells and the 4 Fundamental Unit Cell Shapes

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Primitive1 atom per unit cell (Ex.: ¼ atom on each corner)
Doubly primitive 2 atoms per unit cell (Ex: ¼ atom on each corner and whole atom in center)
Non-primitive more than 2 atoms per unit cell
4 Fundamental Unit Cell Shapes [See slide 10 of Lecture #2]
Square, 'Square Parallelogram', Rectangle, 'Rectangular Parallelogram'
(Can use these 4 shapes to describe any 2-D repeating pattern)

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5 plane lattices

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(clinonet, Diamond net, hexanet, orthonet, square net)

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14 Bravais lattices

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all crystals can be classified into one of 14 Bravais lattices

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Cleavage

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tendency of a crystal to break along planes of weakness (can be PERFECT, GOOD, or POOR depending on quality of the break)

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Fracture

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FRACTURE IS NOT CLEAVAGE occurs when there is NO PREFERRED plane of weakness (irregular, splintery, blocky)

Note: Isotropic minerals have no preferred directions (properties identical in all directions)

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Moh's Hardness Scale and what determines hardness of a mineral

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Hardness is determined by: strength of bonds, density of atoms and size of atoms
Moh's Hardness Scale
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond
^^^(MEMORIZE THIS—insert clever acronym here)

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Silicates

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Silicates arebasic structural unit is silica tetrahedron (SiO4)
most abundant mineral group (b/c O and Si are most abundant elements)
silicates make up 99% of minerals found in igneous rocks

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Different Types of Silicates

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Silicate Subdivisions
Neosilicatessingle silicate tetrahedron (Ex: Olivine—abundant Fe-Mg silicate that is the
major mineral in basalts of ocean basins and mantle)
Sorosilicatespaired silica tetrahedrons
Tectosilicatesframework of silica tetrahedrons (MOST IMPORTANT GROUP)
Feldsparsmost abundant mineral in the crust
Plagioclasesolid solution series
Quartzone of most stable and abundant minerals (O atoms shared in common in framework—strong bonds in all directions and no cleavage)
Zeolitesframework silicates with open structure (cavity or channel)
[IMPORTANT TO ENGINEERING—sieves, ion exchange media, absorbents, remediation, slow release fertilizers and pollution control]
Inosilicatessingle or double chain of silica tetrahedrons (linked by cations)
Pyroxene, Amphibole groups"grab bag" of interstitial ion options
Cyclosilicatesring of silica tetrahedrons
Phyllosilicatessheet of silica tetrahedrons (micas, etc. (see below))

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Characteristics of sheet silicates

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Examples of sheet silicatesmica, biotite, muscovite
Compositionthin layers of silica tetrahedrons (t-sheet) present with sheets of 'octahedrally coordinated' cations (o-sheet, Al, Mg or Ca usually cations for o-sheet)
(sheets form in t-o-t pattern)
Base Exchange Capacitycapacity for cations to exchange in the interlayer region of the structure
Micasno exchange (every 4th silica substituted by Al, so interlayer cations bonded to maintain electrical neutrality)
Kaolinitelimited exchange capacity
Smectitelots of cation exchange (Al and Mg ions as substitutes in the t and o layers allow for greater exchange of interlayer cations as well) charge of sheets is closer to electrically neutral so cations are not tightly held
SMECTITE CLAYS EXPAND DUE TO WATER ADSORPTION

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Oxides

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minerals with oxygen as the anion
Examples: Hematite (Fe2O3, surface of mars), Magnetite (Fe3O4)
Both hematite and magnetite are important ores of iron

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Sulfides

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S2 covalently bonded pairs
Examples: Pyrite (FeS2

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Sulfates

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SO4 is the anion group
IMPORTANT EXAMPLES (of Sulfates)Anhydrite/Gypsum
GypsumCaSO42H2O AnhydriteCaSO4
Gypsum dissolves easily in watersink holes
Anhydrite swellsground swelling
[Transitions back and forth can cause serious problems as clay is hydrated/dehydrated]

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Carbonates

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COx is the functional group
Example: Calcite (CaCO3—used to make concrete)
Dolomite (CaMg(CO3)2—looks similar to calcite, reacts very differently to HCl)

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P waves

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primary wavessub-type of body waves (seismic waves that travel through earth's interior), compressional waves, travel faster through rocks and CAN TRAVEL THROUGH CORE (but waves are bent due to density difference between core and mantle)

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S waves

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secondary wavessub-type of body waves (seismic waves that travel through the earth's interior)shear waves that move side-to-side within rocks, travel slower through rocks and CAN'T TRAVEL THROUGH THE CORE…(led to theory that core is liquid metal)

Note: both types of waves' velocities are affected by material properties of rock
(bulk modulus, modulus of rigidity, density) [See slide 8 of Lecture #3]

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Mohorovicic Discontinuity

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base of the crust…region where the seismic velocities increase sharply—likely due to the transition from crustal rocks to mantle rocks
(mantle rocks are more dense so waves travel faster?)

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Plate Tectonics

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unifying theory of geology, fundamental to how we perceive the world and its dynamic nature [combines several fields of geology (paleontology, geochemistry, geology, geophysics)]
Unifies and Explains: Deformation of crust, Earthquake distribution, Continental drift, Mid-Ocean ridges, Mechanism for the Earth to cool
Two major premises: 1) The lithosphere behaves as a strong, rigid substance resting on the asthenosphere (soft plastic, lubricating layer)
2) The lithosphere is broken into numerous "plates" that are in motion with respect to one another and are continuallly changing shape and size
Seemingly disparate observations from all branches of geology unified under one theory that more easily and better explains the observations

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Natural Remnant Magnetism (mechanism for rock dating)

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Thermal Remnant Magnetismacquired by igneous rocks as they cool. Magnetic minerals are "locked" into an orientation during cooling (Problem: can have overriding magnetism if reheated)
Detrital Remnant Magnetismmagnetic grains aligned with the magnetic field during settling/deposition (mudstone, etc. on bottom of ocean (magnetism re-oriented as they settle))
Chemical Remnant Magnetismoccurs when magnetic minerals grow during secondary processes after a rock forms (Ex: precipitation of magnetite in weathering process)
"Issues with NRM"secular variation: variations in the Earth's magnetic field on time scales < 5 years
Dipole field: axial symmetry of the field means that paleolongitudes cannot be determined
True polar wander: if the true pole position has changed then the position of the calculated paths would change
Deformation: strain on rocks can change NRM, some types can add a later episode of NRM
(becomes hard to tell which episode was first)

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Divergent Plate Margin

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boundary between plates where plate spread apart
Examples: Mid-oceanic ridges (oceanic-oceanic) and Volcanoes on continents (cont.-cont.)
no examples of divergent boundaries between oceanic-continental

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Convergent Plate Margin

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Boundary between plates where plates come together
Examples: Seafloor trenches (oceanic-oceanic or oceanic-continental)
Mountain ranges (continental-continental)
Very active zones for earthquakes and volcanoes due to subduction of crust
(deep earthquake depths)
(Volcanoes form when subducted crust reaches 100km depth of mantle wedge)

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Transform Plate Margin

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Plates slide by each other without either creating or consuming crust
Ex: San Andreas Fault (Shallow earthquake depths, volcanoes very rare)

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Active Margin

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plate boundaries where intense deformation occurs (volcanism, earthquakes, etc.)

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Passive Margin

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edges of continents that are not active margins

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Triple Junction

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distinct form that rifting on continents always takes—3-armed rifts that meet in 120-degree bond angles…typically 1 arm does not result in formation of new crust and is termed the 'failed arm' of the rift [requires localized heat source to form] (Ex: Afar Triangle)

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Deep Sea Trench

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forms along convergent margins when oceanic crust subducts under oceanic crust
trench forms right in front of accretionary wedge just before crust subducts
distance between trench and island arc depends on angle of subduction (distance to reach 100 km depth)

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Accretionary wedge or prism

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along convergent plate boundaries sediments are shattered, crushed, sheared folded and become metamorphosed by the high pressures (form wedge)

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Island Arc

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produced as a result of oceanic-oceanic convergence…when crust reaches 100 km depth magmas are generated which fuel volcanoes that make up the island arc

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Melange

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jumble of large blocks of varied composition and metamorphosed sediments in a mudstone matrix that make up accretionary wedge above a subduction zone (usually made up of mixture of sediments from subducted oceanic crust and continental crust fragments)

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Accretion (in terms of continental growth)

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when all the oceanic crust along the active margin subducts and the continent on the passive margin collides with the one on the active margin
the lighter continental crust doesn’t subduct and the oceanic sediments from the subduction of the oceanic plate are deformed and uplifted when the continents collide (continents grow)

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Igneous Rock

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a rock that crystallized from a magma or lava

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Magma

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molten rock beneath the earth's surface

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Lava

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molten rock on the earth's surface

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Eruption

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when magma reaches the earth's surface and becomes lava

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Pyroclastics (tephra)

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particles that are blasted into the air and carried from the vent of a volcano

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Ash

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smallest pyroclastic particles (< 2mm)

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Lapilli

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midrange pyroclastic particles (2-64 mm)

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Bombs/blocks

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largest pyroclastic particles (>64 mm)

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Intrusive

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igneous rocks that cool within the Earth's crust

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Extrusive

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igneous rock that cools on the Earth's surface (COOL MORE QUICKLY ON SURFACE)

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Phaneritic

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igneous rocks whose crystals are visible to the naked eye—"you can see the bits"
CRYSTALS INDICATE SLOWER COOLING PROCESS

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Aphaneritic

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igneous rocks whose crystals are not visible to the naked eye

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Holocrystalline

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composed entirely of crystals