Exam #2 Flashcards
Atom
the smallest individual particle that retains distinctive properties of a given chemical element
4 major types of bonds
ionic, covalent, metallic, van der waals and hydrogen
Ionic Bond
Electrostatic attraction between (+) and (-) charged ions
Transfer of electron in outer shell to fill void in receptor atom
Produce a moderate strength and moderate hardness bond
Covalent Bond
electrons are shared between atoms rather than transferred
bond is hard and strong
Metallic Bond
Electrostatic attractive force in small group of metals
Electrons in higher-energy level shells are shared among several atoms and very loosely held, so they drift from atom to atom
Forms unique properties: opaque, malleable, good conductors
Van der Waals and Hydrogen Bond
weak secondary attraction between specific molecules
very weak bond
Backbone of minerals
complex ions
4 main methods of mineral formation
Chemically, biologically, cooling from melt, metamorphism
Chemical mineral formation
low T, Supersaturation from fluid or low temperature alteration
Biological mineral formation
low T, Skeleton, external hard parts, internal body, plants, microbes
Cooling from melt formation
high T, Crystalline precipitation from magma
Metamorphism formation
high T, Solid state change (no melting) due to heat, pressure, hot fluids
Are anions or cations larger, and why?
Anions are larger because extra electrons pull on electron less, allowing it to move further from the nucleus
Cations are smaller because fewer electrons make the remaining ones pack together tightly, close to nucleus
Crystal
any solid body that grows with planar surfaces
Crystal faces
planar surfaces that bound a crystal
Crystal form
geometric arrangement of crystal faces; interfacial angles are constant
Growth Habit
characteristic crystal form of each mineral
Luster
the quality and intensity of light reflected from a mineral
Main types of luster
Metallic: polished metal
Vitreous: glass
Resinous: like resin
Pearly: shiny
Greasy: like surface covered by film of oil
Color
determined by chemical composition, but due to ionic substitution, can be misleading for identifying minerals
Streak
color of mineral scratched on an unglazed porcelain plate
Break Cleavage
mineral tendency to break in preferred directions along planar surfaces; crystal tends to break along smooth planar surfaces
Hardness
a mineral’s relative resistance to scratching
High density
atoms are closely packed together
Low density
loosely packed atoms
3 key mineral groups (ALL ANIONS)
Silicate minerals, most abundant in Earth’s crust
Carbonate, Phosphate, and Sulfate
Ore minerals
What clues do minerals provide?
environment of formation
Mineral type gives indication of temperature and pressure of formation
Minerals and their chemistry give clues to climate and weathering, seawater composition
3 main types of rocks
igneous, sedimentary, metamorphic
How does an igneous rock form?
through the cooling and solidification of magma, random interlocking of mineral grains (like a jigsaw puzzle)
Size equals the
cooling rate
Extrusive Igneous rock
When magma cools on Earth’s surface, extruded out, fine crystalline rock and small crystals
Intrusive Igneous rock
When magma cools within existing rocks in Earth’s crust (beneath the surface), you get coarse crystalline rock
Aphanite
fine crystalline rock and small crystals
Phanerite
coarse crystalline rock
What is the mechanism to melt rock and form magma?
increase the heat and reduce the rock melting temperature
What are the 3 basic sources of magma?
basaltic, andesitic, and rhyolitic (BAR)
Basaltic magma
deep in the asthenosphere, mostly ocean crust but some continental
Andesitic magma
mostly subduction zone, ocean-continent type
Rhyolitic magma
mostly continental affinity
Basaltic volcanoes
spreading ridges, within plates in oceanic crust (Hawaiian hotspot) or continents
Andesitic volcanoes
subduction zones, near continents
Rhyolitic volcanoes
beneath continental plates
Partial Melting Theory
Mantle peridotite rock partially melts to form basalt magma (dry process)
Basalt rock partially melts to form andesite magma (wet process)
Andesite rock partially melts to form rhyolitic magma (wet)
Thus, B → A → R (basalt to andesite to rhyolite)
“One Magma Model”
first, everything is melted together, and as it cools, you form different kinds of rocks, and because rocks form at different cooling temperatures, you will form B → A → R
(there are some problems with Bowen’s model, which led to the Partial Melting Theory used today)
Origin of basaltic magma
Comes from partial melting (of peridotites) in the mantle
NO water, so mostly dry process
Less explosive, lava flows
Origin of andesitic magma
Melting near subduction zone
Wet partial melting of mantle rock
Occurs mostly at the edge of continents near subduction zones
Oceanic plate subducts under continental plate
Origin of rhyolitic magma
Continental source
Extrude large amounts of water vapor and water-bearing minerals
comes from andesitic (wet process)
Heat source comes from underlying mantle upwelling
High viscosity, rises very slowly, and solidifies as pressure declines; tends to form large intrusive igneous rocks
Ophiolites
uplifted, exposed fragments of oceanic crust and mantle
Mafic minerals
rich in silica, magnesium, and iron
Usually dark colored
Oceanic crust
Felsic minerals
rich in silica, sodium, potassium
Usually light colored
Continents
What are the big 7 igneous rocks?
granite, rhyolite, basalt, gabbro, diorite, andesite, peridotite
Plutons
bodies of intrusive igneous rock
Minor pluton structures
dike, sill, laccolith
Dike
tabular sheet-like body of igneous rocks that cuts across the rock it intrudes; like a giant wall that runs up and down vertically
Sill
tabular and sheet-like igneous rocks that run parallel to layering or fabric, typically horizontal
Laccolith
similar to sill but layers above intrusion are bent upward into a dome shape
Major pluton structures
stocks, batholiths
Stock
irregularly shaped and relatively small
Batholith
cuts across layering and fabric of the host rock
How do MOST sedimentary rocks form?
from the sedimentation of materials transported in solution or suspension
How are sediments transported?
water, ice, wind, gravity
What is the ultimate fate of most sediment?
burial and conversion to sedimentary rock
3 broad classes of sediments
clastic, biogenic, chemical
Clastic
loose fragments of rock debris produced mostly by physical weathering (gravel, sand, silt, clay - all different sized grains)
Biogenic
composed of fossilized remains of plants or animals
Chemical
precipitates from solution (water)
4 basic classes of clastic sedimentary rock
Conglomerate (rounded) / Breccia (angular)
Sandstone
Siltstone
Mudstone / Shale
Poorly-sorted
wide range of particle size (chaotic, haphazard, various sizes)
Well-sorted
range of grain size is small and uniform
Till
non-sorted (non-rounded) sediment of glacial origin
Cross Bedding
comes from turbulent flow; creates inclined beds in thicker stratum
Graded Bedding
particles are sorted more or less according to size, grading upward from coarser (at the bottom) to finer (at the top)
Rhythmic laminations
varves; a pair of sedimentary layers deposited over a single year (usually in a lake or restricted ocean basin)
2 main ways of forming chemical sediments
evaporative concentration in bodies of water
inorganic precipitation in water
Examples of chemical sedimentary rocks
ooids, evaporites, banded iron formation, phosphate, chert
What is the most important biogenic rock?
Limestone
What do vertical changes in strata show?
passage of time and/or conditions
What do horizontal changes in strata show?
change over distance
Facies
lateral change from one depositional environment to another
Non-Marine modern sedimentary depositional facies
- Stream and river sediments
- Lake sediments
- Glacial sediments
- Eolian (windblown) sediments
Marine modern sedimentary depositional facies
- Deltaic sediments
- Estuarine sediments
- Nearshore sediments
- Offshore sediments
- Carbonate shelves and platforms
- Marine evaporate basins
- Deep-sea fans
- Deep-Sea Oozes
Diagenesis
how sediment becomes rock
Lithification
overall process of creating sedimentary rock
Cementation
substances dissolved in water precipitate out to form a cement that binds grains together
Recrystallization
less stable minerals recrystallize into more stable forms
How do metamorphic rocks form?
Heat and pressure → crystallization → metamorphic rock
What kind of state change is metamorphism?
SOLID, so no liquid is involved
Different types of metamorphism
contact, low grade, medium grade, high grade
6 major factors in metamorphism
Chemical composition of precursor rocks
*Change in T
*Change in P
*Presence or absence of fluids
How long a rock is subjected to high P or high T
Whether the rock is simply compressed or deformed under high P
What is the greatest factor in determining the mineral assemblage of a metamorphic rock?
the composition of the original rock
Low-grade metamorphism
high T but relatively low P; forms slaty cleavage
High-grade metamorphism
high T and high P; forms schistosity
Uniform stress
pressure is equal in all directions
Differential stress
pressure is different in different directions; produces foliated texture
Prograde metamorphic effects
wet process; Metamorphic changes that occur while T and P are rising
Retrograde metamorphic effects
dry process; Metamorphic changes that occur as T and P are declining
Coarse-grained rocks
products of long, sustained metamorphic conditions (millions of years) and high T and P
Fine-grained rocks
products of lower T and P, or in some cases, shorter reaction times
What is the speed of a dry reaction?
very slow because no intergranular fluids present
When does metamorphism STOP?
when the rock starts to melt
Metamorphic rocks formed from shale and mudstone
slate (low), phyllite (intermediate), schist and gneiss (high)
Metamorphic rocks formed from basalt
greenschist → amphibolite → granulite (low → intermediate → high)
Metamorphic rocks formed from limestone
marble
Metamorphic rocks formed from sandstone
quartzite
4 basic settings of metamorphosis
contact, burial, regional, cataclastic
Contact
Dominated by recrystallization due to proximity of magma (not a lot of P or foliation, but high T)
Burial
Dominated by recrystallization aided by water and heat
Regional
Both mechanical deformation and chemical recrystallization
Cataclastic
Dominated by mechanical deformation that leads to physical deformation
“Cataclysmic pieces” (lots of chunks, lots of pressure, stuff going on, mostly high P and low T)
Metasomatism
process in which rock compositions are distinctively altered through exchange w/ ions in solution
Active volcano
eruption since last Ice Age
Dormant volcano
no eruption since last Ice Age but may erupt
Extinct volcano
not expected to erupt
What are volcanoes, essentially?
vents that allow magma to erupt on the surface
What dominates magma composition?
silica
What does thicker magma mean?
more viscous and more gas bubbles trapped inside
Main gases of magma
water vapor and carbon dioxide
Importance of volcanic gases
Influence atmosphere composition
Rates of outgassing controls the violence of eruption (how fast gases come out of solution)
Gas-driven eruptions put dust in the atmosphere, cooling the global temperature
What does viscosity depend on?
temperature and composition
What determines eruptive potential?
gas bubble volume
Phreatic eruption
caused by groundwater flashing to steam in a hydrothermal explosion, magma + water = near-instantaneous evaporation to steam
Pumice
a froth of innumerable glass-walled bubbles
Plinian Eruption
Hot, turbulent mixture rises rapidly in cooler air above vent to form an eruption column
Pyroclasts
all magma and rocks debris that is ejected into the atmosphere from a volcano; subdivided by size
Bombs (largest)
Lapilli (larger)
Ash (smallest)
Lateral blasts
magma forces upward, bulges the flank of the volcano, making the flank unstable and it collapses
Creates huge landslide that removes the side of the volcano, decreasing the pressure on magma, allowing the gas to escape in a massive lateral blast
Blows out rock, pyroclasts, gases, both sideways and upwards
2 broad families of volcanoes
central vent eruptions (mountainous) and long fissure eruptions (come from big crack, not a singular point)
3 classes of mountainous
shield, tephra, stratovolcanoes
Shield
Typical of flowing lava (basaltic), low-viscosity lava
Broad, dome-shaped mound
Tephra
Steep-sided built by successive layers of tephra around central vent
Slope determined by size of pyroclasts
Usually formed in rhyolitic and andesitic volcanoes
Built by pyroclastic debris around a volcanic vent
Stratovolcano
Combo of lava flows and pyroclasts form large, steep, conical mounds
Form classic snow-capped volcanoes
Contain open crater (caldera) at summit
