Geology Exam 2
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Each mineral has a...
Definite chemical composition; internal atomic structure
Sodium Chloride (NaCl)
Halite, tastes like salt
Why study minerals?
- fundamental building block of rocky planet
- rock = mixture of minerals
- form under physical & chemical conditions
- help us understand earth processes
- most metals originate from minerals
- biological processes from minerals as well
seashells & pearls=
bones & teeth=
- calcium carbonate
- phosphate minerals
most abundant element (universe, sun, humans)
oxygen - 50, iron -17, silicon/magnesium - 14
earth's crust comp
oxygen- 47, silicon- 28
earth's atmosphere comp
nitrogen -78, oxygen - 21
lead has high or low density
high density mineral contains...
Lead sulfide (PbS)
Galena, heavy shiney silver metallic
What is Mohs?
Hardness scale, with log scale of absolute hardness on y axis
List the 9 Mohs's hardness scale minerals
colors vary depending on...
Name cleavage of each mineral:
Mica. Florite. Calcite. Quartz
Titanium makes quartz...
Iron makes quartz...
Type of bond is determined by...
....the arrangement of electrons around the nuclei of the atoms involved
electrons transfered.weaker than covalent bonds. ex NaCl
eletrons shared. strongest bond. ex: carbon or water
electrons roam between atoms. makes them conductive and shiney
van der waals bond....
unequal electron distribution around nuclei creates weak charge assymentry. ex "soft" minerals like talc
two minerals that have both ionic and covalent bonds
- Calcite (CaCO3)
- Quartz (SiO3)
the lopsided geometry of water gives it......which allows it to pull apart weakly bonded minerals
a mineral is....
- naturally occuring solid
- usually inorganic
- defined chemical composition
- an ordered atomic structure
a mineral isn't....
- man-made (cubic zirconia or synthetic ruby)
- liquid or gas
- organic compounds (like table sugar or coal)
- amorphis or non-crystalline (obsidian, glass is amorphis and technically a very slow-flowing liquid)
types of atoms =
- bond strength
- atomic structure
controlled by atomic structure (how mobile electrons are within the crystal to affect smoothness; reflect atomic arrangement of atoms)
luster & crystal form
contolled by comp
density & color
controlled by bond strength
- hardness (and atomic structure)
controlled by hardness
diamond versus carbon
various colors, transparent, hardness 10, 3D network of C atoms, electrical insulator
black/gray, opaque, hardness 2, sheets of C atoms, electrical conductor
covalent produces a hardness of....
7 or higher, e.g. quartz
how many minerals are known in the world
elements that come from ore minerals
... out of the 89 minerals make up >99% of earth's crust
most common in earth's crust
most common in whole earth
most abundant and simple silicates
besides silicon, 4 additional elements that add to minerals
Na, Ca, K, Al
most common crustal mineral
3 most important iron-magnesium silicates
olivines, amphiboles, pyroxenes
ions can subsitute for other ions of similar...
carbonates (percipitated out of water, used for cement)
oxides (metals mined and extracted)
halides (percipitated out of water)
sulfates (percipitated out of water
sulfides (mteals mined and extracted)
Type of rock formed from breakdown of pre-existing rocks
rock formed by solidification of molten rock material (magma)
rock formed by the transformation of pre-existing rocks, without melting, because of the effects of elevated pressure, temperature, hot fluid or all 3
....solidify quickly at surface after erupting from volcano (form little to no crystals, often layers)
volcanic/extrusive igneous rocks
....solidify slowly beneath the earth's surface (form large crystals slowly & massive w/out layers)
Plutonic/intrusive igneous rocks
Magma that reaches the surface while still molten is called...
in the weathering process, fragments form....
- clastic sedimentary rock
- ex: sandstone
in the weathering process, dissolved ions form...
- chemical sedimentary rock
- (also is teh cement for clastic rocks)
- the "making of rocks"
- 1.accumulate into beds
- 3.with cements percipitating, form a hardness
alters the shape/orientation of the crystals
changes some minerals into different minerals
metamorphic vs sedimentary
metamorphic vs igneous
- meta - forms in bands (often discountinuous), with light & dark, varying in color and thickness
- meta - has a distict and different mineralogy and no signs of melting
why know igneous rocks & process?
- locate valuable minerals
- learn more about earth's internal processes such as plate techtonics
- avoid hazards from volcanoes
name 5 intrusive structures
- magma chamber
- dike (shallow errosion, cuts across layers)
- sill (cuts horizontally between layers)
- volcanic neck (devil's tower)
- batholith (deeper erosion)
igneous rocks are classified by...
composition (minerals present): glassy, aphanitic, porphoritic, phanaritic
texture (size of crystals): ultramafic, mafic intermediate, felsic
where do igneous rocks form?
- divergent boundaries/hot spots (decompression )
- convergent boudnaries (adding water)
The magma has the same composition as the original rock when....(and can recrystallize)
the rock melts completely
the relationship with temperature increase with increasing depth into earth
- Geothermal Gradient
- beneath continental crust: 30* C per km
- beneath ocean crust: 60* C per km
early-forming crystals will either settle downward or attach to the walls where the temp is coolest and grow inward. Magma changes composition continuously.
describe the volcano types
most explosive volcano is...
Composite (mt st helens) b/c of the gas build up
gases escape more readily from ....magma
viscosity = resistance to flow; depends on composition
high silica vs low silica
- high silica = high viscosity = thicker= explosive eruptions=cascade volcanos=felsic
- low silica = low viscosity =runnier = quite fluid flows = basalitc sheild volcanoes (hawaii) = mafic
order common igneous rocks by high to low silica content/viscosity
describe volcanic gases
- SO2 reflect sun's energy back to space and cools the earth's temperature
- contain Pb, As, Au, Hg, etc
The more silicate rich the magma the .... the gas content
elaborate on 8 volcanic eruptions:
- Lava flows: pahoehoe vs. a’a
- 1) volcano-tectonic = magma movement
- 2) long period = volcanic tremor
- Landslides/Tsunamis: eruption not required
- Volcanic gases: precursor to eruption; VOG
- Directed blast: structural weakness (Mt. St.Helens)
- Pyroclastic flows: “nuee ardentes”; surges
- Lahars: eruption not required;(mud/debris flow) composite volcanoes
- Tephra/Ash fall: acute (asphyxiation) andprolonged hazard (climate change)
What VEI rating does a super volcano have?
- Volcanic Explosive Index
Composition = extrusive/intrusive
Name according to comp...
- Ultramafic = very rare/peridotite
- Mafic = basalt/gabbro
- Intermediate = adesite/diorite
- Felsic= Rhyolite/granite
increase in pressure......melting temperatures
- this means rock moving upwards tends to melt
felsic magma density is ....than crust density
mafic magma density is.....than crust density
mafic magma density is .....than MANTLE density
- less than
- greater than
- less than
why study sedimentary rocks?
- contain archive of ancient history of the planet
- preserve fossils
- derive coal, oil & natural gas
- open spaces btwn sedimentary layers acts as storage for water/oil/natural gas
physical weathering often takes advantage of....
- irregularities in rock
many minerals readily dissolve in water, especiialy those with....bonds
chemical weather occurs 3 ways:
most abundant clastic materials
calcite dissolves better ....water and comes out in ....water
silica dissolves ....water and comes out in ....water
- cool water; warm water
- warm water; cool water
most important mineral cements
Sedimentary rock classification determined by texture and composition
Texture determines ........nomeclature.
Composition dominates .....nomeclature.
- Clastic (grain size, sorting, rounding)
freeze/thaw, root wedging, jointing
dissolution, hydroysis, oxyidation
classification (grain size, sorting, & rounding) allow scientists to interpret....
sediment source, weathering and erosion history
clastic sediemtn texture reatlates to...
- strength and steadiness of currents transporting the sediment
- distance of transport
3 main types of preservation in sedimentary rocks:
- original materials such as bones/teeth
- minerals replace carbon-rich compounds
- as an impression that remains in the sediment such as footprints/shell casts
fossil fuels (stored chemical energy from sun) form from....
organic matter disposited by sediments (plants/animals)
locating fossil fuels requires a knowledge of sedimentary rocks
the characteristics used to name sedimentary rocks can be used to interpret the history of an area that was once a lake, beack, swamp, etc.
graded beds implies....
shale layers in between indicate...
- settling of coarse then fine particles
- sediment being swept by waves before it settled
- times of slow accumulation
graded sandstone beds interlayered with deep water marine shale are the result of.....
metamorphic rocks are found in....
- activiely forming mountain ranges
- always in eroded mountain belts
metamorphic rocks exhibit two types of change
- new minerals form
- rock texture is altered
raising the temperature of rock through sediment burial, tectonic burial, and magma intrusions allow the material to reach...
high temp metamorphism causes...
- mineral states are stable at a fixed range of temp and pressure
- ex: water as a liquid, solid, gas
geothermal gradient for metamorphism: temperature increases as rocks are .....in earth's crust
recrystallization of minerals into new ....and .....
recrystallization changes rock texture without changing ... and ...
- without changing:
- chemical comp
- mineral content
describes planes of mineral formed in response to stress
the presence of ... makes metamorphic reactions occur faster and more easily.
...are those that form in a limited range of conditions
tell the geologist about the metamorphic conditions (b/c they're stable over a certain temp/pressure)
- good:chlorite(low),amphibole, pyroxene
- poor: quartz, feldspars, muscovite
metamorphic texture is foliated or non-foliated. define....
composition depends on ... and ...
- foliated rocks all have layered minerals
- parent rock and fluids
Order foliated metamorphic rocks by lowest grade:
non-foliated metamorphic rock is named by its ..... as the primary characteristic
composition (mineral content)
most common contact metamorphic rock
contact metamorphism: metamorphic grade is highest when it is located .....to the intrusion
occurs along the boundaris of igneous intrusion and under lava flows
heat is dominant agent
....occurs along mid-ocean ridges/divergent plate boundaries
involves migration and raction of hot, mineral rich geopthermal FLUIDS
...occurs along subduction zpones and active mountain-forming zones
...occurs on a broad, large-scale
....is pressure driven
in regional metamorphism:
low-t/high-p occurs when parallel and ....to trench
high-t/low-p occues when parallel and ....to trench
paired metamorphic belts refere to .....metamorphism
protolith or parent rock transformation in metamorphic rocks:
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