EXAM 2 MATERIAL Flashcards
when did petrography begin and who invented it?
- 1828
- william Nichol
How was petrography invented/developed?
Polarized light was produced from by cutting Iceland spar, a variety of calcite, into a prism.
what is the idea thickness of a thin section?
30 microns
what technique did henry Sorby develop?
-cutting rocks into thin slices, affixing them to a microscope so light could be transmitted through the crystal
what is a minerals’ refractive index?
how much the velocity of light slows when it passes through a crystal
how is refractive index calculated?
(the velocity of light in air)/(the velocity of light in the mineral)
how are refractive indices measured?
a device known as a refractometer
what is the angle of refraction?
the angle made by a refracted ray of light
define Snell’s law
sini/sinr=RI2/RI1
what is the angle of incidence
describes the angle light impinges on the boundary
what range of the electromagnetic spectrum is visible to the human eye?
400-700 microns
what is the velocity of light in a vacuum?
300,000 Km/s
is the speed of light the same in all materials?
NO, it slows thus resulting in the light ray bending (refraction)
what is retardation of light in minerals?
a function of the thickness of the mineral
what is the range and color of first-order interference colors?
red at 550 is first order interference color
0-550 nm
what is the range and color of second-order interference colors?
blue is second order interference color
550-1100 nm
what is the color of third-order interference colors?
pink
what is the nm range associated with each order color?
550 nm
Do isometric crystals exhibit interference colors, why or why not?
NO, crystals have three axes of equal length
what are isotropic materials?
have only one refractive index and are independent of the path of light
what is birefringence
the difference between the minimum and maximum index of refraction
why do interference colors exist
as the N-S fast and slow vibrating waves pass through the upper polarizer, they are out of phase, causing interference and their resulting colors.
what is extinction in minerals?
light is completely eliminated by the upper polarizer, appearing dark.
GO BACK TO ANISOTROPIC/ISOTROPIC SECTION (CH. 6)
are extinction angles important in mineral ID?
YES
what are fast and slow vibration directions related to?
promoninent crystallographic characteristics: cleavage, twinning
how can fast and slow vibration directions be measured?
with the use of an accessory plate
how is pleochroism observed?
in polarized light, the color of a mineral changes depending on the orientation of the crystal
what causes pleochroism?
the absorption of different wavelengths of light in different directions
is pleochroism a useful diagnostic property?
YES
what is the difference between a uniaxial and biaxial optical indicatrix
uniaxial has one optic axis biaxial two optic axes
which crystal classes have biaxial optical indicatrix and how many RI do they have?
- orthorhombic
- monoclinic
-triclinic
THREE RI
what are there two types of optical indicatrix?
- uniaxial
- biaxial
which crystal classes have uniaxial optical indicatrix and how many RI do they have?
- tetragonal
- hexagonal
TWO RI
what is the optic angle designated as?
2v
what is the optic angle measuring?
the acute angle between two axes
What is modal analysis
the areal abundance of a mineral
what techniques are involved in modal analysis?
comparing what is observed in thin section to a chart showing typical abundances
TERNARY diagram- CH7 slide 10
know how to solve and know how to normalize and plot lines on diagram
what percentage abundance must a mineral be to be considered major elements
more than 1 wt.%
what percentage abundance must a mineral be to be considered minor elements
1.0-0.1 wt%
what percentage abundance must a mineral be to be considered trace elements?
less than 0.1 wt%
what is the importance of silicon and oxygen in rock forming minerals?
the crust is made almost entirely of oxygen and silicates
BINARY DIAGRAMS- CH7 (slide 7)
calculation of mineral formulas
what is the difference and similarities between fayalite and forsterite as far as composition?
- both end members of olivine
- Fe rich= Fayalite
- Mg rich= forsterite
be familiar with the calculation steps in determining mineral formulas
ch 7 slide 8
what are tie lines and what do they represent?
horizontal lines connection two coexisting phases
how can igneous minerals be structured in a 3d manner
tectosilicates
what is the only SiO2 mineral that does not contain tectosilicates?
stishovite
what group has single chain silicates?
the pyroxene group
what group has double chain silicates?
the amphibole group
what are both chain structures known as?
inosilicates
what are sheet silicates known as?
phyllosilicates
what are double tetrahedra silicates known as?
sorosilicates
what are the different types of silicate structures?
- infinite networks
- infinite sheet
- single chain
- double chain
- double tetrahedron
- Independent tetrahedra
what are independent tetrahedra silicates known as?
nesosilicates OR orthosilicates
what are ring structures known as?
cyclosilicates
what are the three polymorphs of k feldspar
Microcline, orthoclase, sanidine
how are the three polymorphs of kfeldspar DIFFERENT from each other?
in microcline: Al position is ordered
in orthoclase: Al position is partial ordered
in sanidine: Al position is totally disordered
can quartz and nepheline coexist stably in the same rock why/why not?
NO
nepheline in undersaturated in silicon, but quartz is silicon rich
rocks with modal quartz are considered______________?
silica oversaturated
rocks with modal nepheline are considered______________?
silica undersaturated
what makes feldspathoids unusual?
similar to feldspars in structure and appearance. but contain much less silica.
what is the major difference between orthopyroxene and clinopyroxene?
- orthopyroxenes are orthorhombic
HIGH Ca - clinopyroxenes are monoclinic
LOW Ca
invarient pointss, univariant lines GO BACK AND REVIEW
in order for equilibrium to exist, what gradients must be eliminated?
- system
- temperature
- pressure
- chemical
what is Gibbs phase rule equation?
f=c+2-Φ
what are phases and how are the denoted in the Gibbs phase rule?
individual minerals, liquids and gases
denoted by the Greek letter Φ (phi)
what are components and how are they denoted in the Gibbs phase rule?
the minimum number of constituents needed to describe the phases present
denoted by the letter c
what are degrees of freedom and how is it denoted in the Gibbs phase rule?
how many variables can be changed without changing the phases present. denoted by the letter f
what is the Maximum number of phases a rock can contain when there are 0 degrees of freedom (f)?
number of components present plus 2 (c+2)
what is the Maximum number of phases a rock can contain when there is one degree of freedom (f)?
number of components plus 1
(c+1)
what is the Maximum number of phases a rock can contain when there are two degrees of freedom (f)?
number of components is equal to the number of phases
(c=Φ)
what happens to the freezing point of a solution if salt is added to water, is there a limit?
the freezing point is depressed.
YES
what does a liquidus line represent in a salt-water phase diagram?
above the line is salty water, below the line, ice and salty water are in equilibrium
does a salt-water phase diagram have a solidus line?
NO
what does the eutectic represent in a phase diagram?
the lowest possible temperature at which a liquid can exist
what is meant by the term liquidus?
all components are liquid
what is meant by the term solidus?
all components are solid
what is the effect of two minerals present together and how do they effect each other
the minerals dissolve into each other, lowering their melting point
what is the lever rule and what does it allow us to do?
allows the determination of mineral wt percentages graphically
what is a solvus line?
a line the separates a solid phase from a solid1 + solid 2 phase
what is exsolution
the separation of one mineral from another
how is exsolution observed in alkali feldspars?
perthite texture
how does adding a third component to the eutectic fluid effect solution AB
it lowers the liquidus of AB
what is the difference between binary and ternary eutectics?
binary eutectics contain two components
ternary eutectics contain three components
Why does a ternary eutectic occur at lower temperature than the binary eutectics?
because it has more components=lower crystallization temperature
how does the earth seek a state of equilibrium?
by eliminating gradients in intense variables
what is transport law and its two required components?
laws governing transport rates
1- the driving force
2- the resistance term
what is darcys law
describes fluid flow through a porous medium
what is viscosity
the property of a fluid to resist flow when stress is applied
what is fouriers law
describes the flow of heat by CONDUCTION ONLY
what is fricks law
describes the diffusion of atoms
what factors control viscosity
temperature
when were the first absolute age estimation of earth materials produced AND by whom?
1907
Bertram Boltwood
what did kelvin theorize about the age of the earth. why was it INCORRECT?
he said the earth could only be 100 Ma.
he theorized that the earth was losing its initial heat and could not generate its own. obviously not correct
what are the four types of radioactive decay?
- Alpha
- Beta
- Electron capture
- fission
what is alpha decay and what is an alpha particle?
neutron ejects and alpha particle
contains 2 protons and 2 neutrons
what is beta decay?
a neutron changes into a proton by emitting an electron (beta particle)
what is electron capture decay?
electrons are captured by a nucleus, combines with a proton to create a neutron
what is fission decay?
splitting of the nucleus into to equal sized, nuclei
how is absolute age calculated using decay formula?
age= # of half lives X decay constant
calculate an age give a parent:daughter of 1:15 and a half life of 10 Ma
40 Ma
what are half lives
the amount of time it takes for an amount of radioactive material to be halved
what are decay constants
proportionality between size of radioactive atoms and the rate at which they decrease
what is blocking temperature
the temperature at which ions are no longer able to go into or out of a crystal
what does radiometric age tell us
estimate how long ago rocks were formed
where do melting processes occur?
divergent margins
- M.O.R
what drives volcanism?
the ability to melt mantle and magma to ascend to the surface
what drives magma ascent?
magma is less dense than the rock it formed from, therefore it rises
what are the types of intrusive bodies of magma?
dikes
sills
what is underplating
the addition of material (usually from the mantle) underneath a tectonic plate
what kind of rock does silica rich magma produce?
andesite
where does most melting on earth occur?
decompression at M.O.R
name three magma sources (could be a location or a process)
1- decompression at M.O.R
2- mantle wedge above subducting plates
3- heating associated with mantle hot spots
how can different types of rocks form from a single parent magma?
- magmas cooling slowly
- assimilation
- fractionation
what are mantle xenoliths?
pieces of the mantle brought to the surface through magma movement. IMPORTANT.
at what depths are aluminum bearing minerals stable in mantle
20-400 kilometers
what is the role of volatile content on melting?
- lowers melting temperature
- high gas pressure causes more explosive eruptions
what are the three ways melting can occur?
- raising temperature
- lowering pressure
- adding water (lowers melting temperature)
what is the difference between hydrous and anhydrous melting?
hydrous melts contain water molecules MORE COARSER GRAINED
anhydrous melts are finer grained
what are the most abundant volcanic gases being emitted at the surface
- water
- CO2
what is the importance of magma density/ density contrasts
- drives tectonic plates and magma movement.
- density contrast between crystals can change magma composition
what controls magma density?
composition
how is rock conductivity related to heat flow?
different rocks have different thermal conductivity
can heat transfer be related to convective flow in magma bodies
yes, convection dramatically increases cooling rates
what does settling velocity refer to?
how quickly crystals can settle in a melt
what is stokes law used for?
used to calculate settling velocity
what are the most important factors in settling velocity
crystal size and density
what is laminar vs turbulent flow
laminar is low energy, turbulent is high energy
what is fractionation
the separation of crystals from the liquid
what are cumulates
rocks formed by the accumulation of crystals
what is the origin of isotopic reservoirs, how do they evolve
originate via:
- planetary differentiation
- chemical reactions
evolve via:
- magmatic processes
- radiogenic isotope production
what is modal layering
rocks showing layering of minerals
what is assimilation by reaction
rock change the composition of magma by reacting with it, not melting
