Earth Materials Exam Two

Name three chemical analysis of minerals methods

wet chemistry, scanning electron microscope energy dispersive analysis, electron microprobe wave-length dispersive analysis

How is Wet Chemistry analysis completed?

mineral is grinded and physically separated, sample is dissolved in acid

what are the main parts of scanning electron microscope

electron gun, focusing lenses, sample chamber, detectors

what are the detectors in scanning electron microscope

secondary electrons, backscattered electrons, cathodoluminescence, electron backscattered detector, energy dispersive x-ray detector

what are the four ways an electron beam interacts with a sample

backscatter electrons, secondary electrons, x-rays, light (cathodoluminescence)

what happens with backscatter electrons

electrons bounce back, sensitive to density with denser samples being brighter

what happens with secondary electrons

interactions with valence electrons, sensitive to topography, generates 3D images

what happens with x-rays

electrons remove electrons from inner orbitals, electrons from higher orbitals fall in and x-ray is generated, wavelength and energy is quantized based on the energy levels of orbitals

what happens with cathodoluminescence

light is given off when bombarded with electrons

brightness depends on density with backscatter electron image. denser minerals are ___ and less dense are ___

bright, dark

elements with 1 peak are what kind of radiation

Ka

elements with 2 peaks are

Ka and KB

intensity of peak is proportional to what

amount present

Who created the Rowland Circle Geometry

Henry Augustus Rowland

with Rowland Circle, you can change the position of the crystal and detector to obtain a different ___

incident angle; to get a different element of interest

secondary electrons gives images of surface ___

topography

backscattered electrons gives images of

mean atomic number

calcium x-ray map

diffracting crystal is used to detect Ca Ka x-rays

cathodoluminescence image

a few elements emit visible light when bombarded with electrons. bright bands are a specific color and probably reflect relatively high dysprosium concentration

use WDS X-ray mapping to

collect elemental “maps” showing the distribution of an element within a crystal

if a “random” nucleus has a radius larger than r*, the nucleus will (grow/not grow)

grow

if a “random” nucleus has a radius smaller than r*, the nucleus will (grow/not grow)

not grow

what is overstepping

deltaG being slightly off of equilibrium; off of temperature=pressure

why is nucleation favored by large degrees of overstepping?

rate of nucleation depends on the amount of overstepping (affinity)

what are 3 ways to achieve overstepping

changing temperature and/or pressure, cooling below freezing curve, supersaturation of a vapor or liquid

What are the 4 main ways minerals can form?

solid-solid reactions, crystallization from a liquid, deposition from a vapor (no intermediate liquid), precipitation from a fluid such as H2O or CO2

what does polymorph mean

minerals in different forms with the same composition but different structures

what is polymorphic transformation/solid-solid reaction

when one polymorph transforms into another

what controls the conditions which a particular polymorph is stable?

temperature and pressure

name 3 polymorphs of SiO2

quartz (trigonal), tridymite (triclinic), cristobalite (tetragonal)

name 3 polymorphs of Al2SiO3

kyanite, sillimanite, andalusite

draw the Al2SiO3 phase diagram

what are the 3 energy states

unstable, stable, and metastable

what is Gibbs Free Energy

measure of chemical energy, all chemical systems tend naturally toward states of minimum free energy

At higher temperature, the phase with larger entropy (S) will have (higher/lower) G

lower

at higher pressure, the phase with the lower volume will have the (higher/lower) G

lower

smallest volume means (highest/lowest) pressure

highest

largest volume means (highest/lowest) pressure

lowest

largest entropy means (highest/lowest) temperature

highest

smallest entropy means (highest/lowest) temperature

lowest

which mineral has the smallest volume?

stishovite

which mineral has the largest volume?

tridymite

which mineral has the smallest entropy?

alpha quartz

which mineral has the largest entropy?

liquid

what are the 2 polymorphs of CaCO3

aragonite and calcite

what are the 3 types of polymorphic transformations? with examples

reconstructive transformation (quartz to coesite, kyanite to sillimanite), displasive transformation (alpha quartz to beta quartz), order-disorder (sanidine to orthoclase to microcline)

give the mineral names of an example of solid-solid reaction involving more than one phase

albite, jadeite + quartz

which indicates higher pressure?

jadeite + quartz

which has a smaller volume?

jadeite + quartz b/c the pressure is higher

what is nucelation

formation of new minerals

why do displasive and order-disorder transformation NOT require nucleation?

bonds stretch or shrink but do not break in displasive transformation (beta-quartz to alpha-quartz)

atosm order on different crystallographic sites in order-disorder (sanidine to orthoclase to microcline)

what are the five types of bonding found in minerals

ionic, covalent, hydrogen, metallic, van der waals

which is larger, O(2-) or Si(4+)

O(2-)

what are the 6 common coordination polyhedral found in minerals?

2 fold (linear), 3 fold (planar), 4 fold (tetrahedral), 6 fold (octahedral), 8 fold (cubic), 12 fold (dodecahedral)

what does Pauling’s first rule say about ionic radii of anions and cations?

Rc/Ra controls type of coordination for an anion-cation pair

who discovered X-rays

Wilhelm Rontegen

what is reflection

bouncing of waves

what is refraction

change in direction of waves

what is diffraction

waves spread out

when diffraction grating was too coarse to diffract x-rays, what was suggested

crystal lattice with smaller spacings

why are x-rays used in determining crystal structures

wave lengths are 0.01-10nm, similar to the atomic distances between layers in crystalline solids

what is the order in the electromagnetic spectrum

radio, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays

what happens in x-ray generation

incident electron ejects “inner shell” electron, an electron from higher-energy shell drops “down” to fill the vacated position

how are x-rays made

bombarding a material with electrons

what is the relationship between wavelength and energy of electromagnetic radiation

E = hv or E = hc/λ. E and λ are inversely proportional

what are the two ways waves interact and how

destructive waves cancel each other out and constructive waves add to each other

what is Bragg’s law and what is it used for

nλ = 2dsin

Bragg’s law gives the relationship between wavelength, d spacing of a set of planes in a crystal lattice, and the angle of incidence

it specifies the conditions where x-ray diffraction will occur

do x-rays have longer or shorter wavelength than visible light

shorter

do x-rays have longer or shorter wavelengths than ultraviolet light

shorter

what do peaks represent in power diffraction patterns

each peak corresponds to a specific d spacing of planes in a crystal lattice

what are the 7 arrangements of SiO4 tetrahedra in silicate minerals and how are they linked together

isolated, pairs, rings, single chains, double chains, sheets, network

what happens in ionic bonding

one element gives up an electron and another element gains it

what happens in covalent bonding

electrons are shared

what happens in metallic bonding

valence electrons are given up and ionized and delocalized

what is the main characteristic of van der waal bonds and hydrogen bonds

they are very weak because of uneven charge distribution in the atoms

what are Pauling’s Rules

1) radius ratio principle

2) electrostatic valency principle

3) edge and face sharing are unstable

4) cations of high valence and low C.N. tend not to share anions with other cations

5) principle of parsimony

what is the Rowland Circle used for

to focus x-rays emitted from a sample for a single x-ray wavelength for chemical analysis

change the position of the crystal and detector to obtain a different theta angle

when a mineral is bombarded with electrons, what radiation does it give off

secondary electrons, back scattered electrons, and x-rays

why is scanning electron microscope (SEM) or electron microprobe (EMP) more useful than wet chemistry

wet chemistry requires a mineral separate, which might not be pure

wet chemistry makes a bulk analysis but the mineral might be zoned

wet chemistry is destructive (uses up all the material)

SEM and EMP are spot-sensitive, non-destructive, and can be used to determine zoning

what 2 related characteristics of x-rays are used to determine the composition of a mineral

wavelength and energy

what is a mole

unit of measurement for amount of substance, refers to the number of particles, amount of substance containing the same number of molecules

which has more “units of quantity” a mole of SiO2 or Al2O3

same moles because both equal 6.022×10^(23)

which has more “units of quantity” mole of SiO2 or mole of Si2O4

Si2O4 has more because it is double

what are the 3 major divisions of Earth structure

core, crust, mantle

what are the most abundant rock types in the crust

95% igneous and metamorphic rock

what is the average composition of the continental crust

oxygen, silicon, aluminum

what is the average composition of continental crust

granodiorite

what is the most abundant mineral in the crust

plagioclase, alkali feldspar, quartz

what is the most and second most abundant element in the crust

oxygen, then silicon

what are the three most abundant elements in the mantle

oxygen, silicon, magnesium

which are typically larger, anions or cations

anions

what is a coordination number

number of atoms bonded to a central atom

what are the feldspar polymorphs from disorder to order

sanidine, orthoclase, microcline

name the polymorphs of SiO2

alpha-quartz (low quartz)

beta-quartz (high quartz)

Tridymite

Cristobalite

Coesite

Stishovite

what are some examples of nucleation

rain forming in a cloud

ice forming on a pond

bubbles in your soda

differentiate homogenous vs heterogenous nucleation

homogenous is spontaneous in a clean environment, and is energetically more difficult

heterogenous is on top of an existing phase, and is energetically easier

what is meant by “overstepping”

measure of how far we are from equilibrium (T, P, or composition)

what is nucleation

formation of a new mineral (phase)

why is nucleation favored by large degrees of overstepping

rate of nucleation depends on amount of overstepping

the larger deltaG, the smaller critical radius, and nucleation rate will increase

what are 3 ways to achieve overstepping

changing temperature and/or pressure

cooling below freezing curve

supersaturation of a vapor or a liquid