Lecture Flashcards
(60 cards)
1
Q
Minerals definition
A
- natural occurring solid with a definable chemical composition and a crystalline structure (orderly arranged atoms)
- definable chemical composition: can be used expressed using formulas but composition are not fixed.
Note: liquid and gas not considered minerals
2
Q
Minerals definition
In summary:
- naturally occurring solid
- definable chemicals composition
- crystalline structure
A
- natural occurring solid with a definable chemical composition and a crystalline structure (orderly arranged atoms)
- definable chemical composition: can be used expressed using formulas but composition are not fixed.
Note: liquid and gas not considered minerals
3
Q
Crystalline structure
A
Crystalline
- in term of atomic arrangement exactly same through out equivalent to 200 degree at 10-10m eg
- not randomly distributed
Amorphous
- lack internal atomic arrangement, not orderly arranged. Eg obsidian( volcanic glass)
- are randomly distributed
4
Q
Biological activity can facilitate mineral formation
-they are all calcium carbonate but differently arranged
A
Eg calcite and aragonite are polymorphism
Calcite: occur in the trioriginal system
Polymorphism:
- same atomic composition but different atomic structure. Eg graphite and diamond are also good example.
5
Q
Macroscopic properties of mineral
A
- we can see with naked eyes or hand lenses due to composition and structure makes them important.
- helps to determine the composition of the minerals
6
Q
Mineral identification
A
- a skill requires diagnostic properties
7
Q
Physical properties of minerals
A
- lustre
- crystal habit
-hardness - streak
- color
- specific gravity fracture or cleavage
- fracture or cleavages
8
Q
Lustre
A
lustre: property of light reflected or scattered from the mineral surface ( two subdivisions
1. Metallic ( reflecting light)
2. non metallic ( sub-vitreous or dull) or glass like
Ex: pyrite :a crystal with well developed faces ( euhedral)
Subhedral: crystal aggregate of pyrite
9
Q
Crystal habit
A
crystal formation eg poorly formed or well-formed, aggregate of well- formed minerals
10
Q
Hardness of mineral
A
hardness:
- measure of density/ scratch resistant. Moh scale for hardness
11
Q
Streak of minerals
A
streak: mineral in powdery form by scratching mineral on unglazed porcelain
- streak color is less variable than crystal color
- obtains by scratching
12
Q
Color
A
- color ( is physical properties but not use for diagnostic properties)
- Color is part of light that is not absorbed by mineral.
- combination of diff wavelengths not absorbed
- often reflect trace impurities
13
Q
Specific gravity
A
specific gravity fracture or cleavage:
- measure of density of mineral
- we use heft to measure density of mineral
14
Q
Cleavage
A
- tendency to break along planes of weaker atomic bond
- produce a flat, shy surfaces. It’s repetitive through mineral, often formed parallel steps
- sometimes mistaken for habit
15
Q
Fracture
A
- discription of quality of surface other than cleavage plane along which mineral break with sufficient force is applied.
16
Q
Twining
A
- some crystals have a twining station
-contact twin ( eg calcite, spinel, japan to twin quartz)
- albite twin
- penetration twin( Carlsbad , fluoride, pyrite deal, staurolite twins)
- cyclic twins ( chrysoberyl, pseudo hexagonal twin of orthorhombic aragonite)
17
Q
Other physical properties
A
Effervescence: reaction with acid ( calcite)
Magnetism: magnetic attraction
Taste: self -explanatory ( salt like halite)
18
Q
Lecture 3
A
19
Q
Mineral
A
- more than 5000 are know
- systematic study of mineral therefore requires some mean of classifying them
20
Q
Two ways of classifying minerals
A
- structure
- classification based on chemistry is most way used which are
- anion (-ve)
- Cation (+ve)
Group differs in proportion of cation and anions within a group similar combination of cation of anions
21
Q
Oxides
A
Three main based metal cation/ oxygen ratio
- hematite group X2O3 hexagonal
- rutile group: XO2 x- +4 cation most phase tetragonal
- Spinel group; XY2O4 X- + 2 ; Y- + 3 cation most phase isometric or orthorhombic
22
Q
Mineral series
A
- solid solution
- composition of variation arising between species due to substitution of one cation for one another
- mostly cation substitution not anions
Ex: olivine containing 100% forsterite ( 100% mg end member) and 100 % fayalite ( 100% fe end member), any forterite/ fayalite in the middle are olivine but 50% fo and 50% fe - all are called olivine minerals series
23
Q
Other silicate
A
- abundant minerals on earth crust
- non silicate are few %
- formed 92% of mineral contains silicate on earth crust
- reason was that the chemical composition of minerals on the earth crust like O2 are too dominant in the crust and we can see that most of the minerals behave like silicate
24
Q
What constitutes silicate
A
- is because Oxygen and silicon bond together
- forming coordination tetrahedral
- silicon tetrahedral is the fundamental units of silicate minerals
25
Classification of silicate minerals
- Why does silicate diverse group of mineral
-looking at the valence of electron, oxygen is anion has a charge of two if sum up all oxygen we get total charge of 2
- silicon is cation has net negative charge
- because some of the energy available of oxygen not satisfied by the silicate. Minerals don’t exist that way, u can’t have excess charge to compensate for that, silicate bond to oxygen.
26
Neso silicate (single chain)
- silicate tetrahedral not connecting oxygen to other silicates tetrahedral called neso silicate or tetrahedral silicate or orthosilicate ( not sharing oxygen to other silicate) because they are granulated, unshared bond coz they are not connected to each other
- unit composition = sio4 equivalent to 1si ratio 4 oxygen (1:4)
(Mg,fe)2sio4
- independent tetrahedra
27
Sorosilicate (disilicate)
(SI2O7)6-
-sharing two silicate tetrahedral shared 1 oxygen
(Si2O7)6- = 2:7 of silicate oxygen
- ex: hemomorphite Zn4si2O7(OH)2 . H2O
28
Inosilicate(single chain)
(SI2O6)4-
-they are single chain
- have two oxygen shared
- pyroxene
- ratio 1:3
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Cyclosilicate ( SI6O18)^12-
-they are circle like
- unit composition equal ( SI6O18)^12-
- ratio 1:3
- ex is bery Be3Al2SI6O18
30
Phyllosilicate( sheet silicate)
- each silicate tetrahedral sharing 3 of its oxygen with neighbours. Alternate one sharing 2 oxygen
- composition unit = SI2O5)^2-
- Ratio= 2:5
- example =mica eg phlogophite, KMg3(AlSI3O10)(OH)2
- 2D structure
31
Tectosilicate
- formed 3D-structure
- all oxygen shared with neighbouring tetrahedral
- SI:O ratio = 1:2
- example: quartz, feldspar
32
Unit cell
- small volume is repeated through the crystals
- has geometric( symmetric) properties, physical properties and chemical properties.
- can be defined by three vectors a,b,c and three angles Alfa , beta and gamma
- between z and y is vertical axis called Alfa
- between y and x is horizontal called gamma and between z and ,x is called beta.
33
Minerals can be divided into into one of Seven crystals system based on the shape of unit cell
1 isometric/cubic = all three axis are equal and perpendicular to one another.
- a1=a2=a3 are crystallographic axis
- (Alfa = beta= gamma) =90 degrees
- Also octahedral has similar properties
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2. Tetragonal
- two of the three axis are equal in length, and all three axes are perpendicular to one another.
- a1=a2 not equal c
- angle are still same 90 degree
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Orthorhombic
- unequal thee axes but perpendicular to one another. a not equal b no equal c
- still have angle at (Alfa =beta=gamma)= 90deg
- crystal system in which all the three axis are unequal in length but still have all angle perpendicular to one another at 90 is called polymorphic.
36
Monoclinic
- all three axes are unequal a not equal to b not equal to c
- the three angle not perpendicular but two are perpendicular Alfa=gamma=90; Beta not at 90
-one axes is inclined
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Triclinic
- none of the axes length are equal a not equal b not equal c
- none of the angle are perpendicular Alfa not equal beta not equal gamma
38
Rhombohedral also trigonal
- all the axes are equal length a=b=c
- all three angles are equal (Alfa =beta = gamma) but all three not at 90
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Hexagonal
- 4 axes, three equal length separated by equal angles (Alfa =beta = 90) and gamma=120
- 4th axes perpendicular to the plane of the other three axes
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Lecture 4
Microscopy and light properties
41
Importance of microscope
- used to measure small/ tiny particles of minerals
- can resolve things up 100um
42
White light
- has wavelength of approximately 409-700nm
43
Wavelength and amplitude
- wavelength is a distance between crest and trough
- amplitude is the magnitude of vibration. Also vibration perpendicular to to the vibration direction and to the maximum vibration
44
Ordinary light
- has speed of 3x10^8m/s in vaccum without interacting with any particles
- any other materials eg air, water , minerals or atoms etc speed of light may be slower coz those waves can’t interact with electron in the matter. As the light travels through it excite the electron and electron start vibrating. Some energy in the light waves is transfer to electron in the material and in the process the light speed slow down. In general speed of light = (wavelength multiply by frequency).
- When light slows down the frequency remains Same.
- in most material light have slower speed in vacuum which is index of refraction = (ratio of velocity velocity in vaccum/ ration of velocity in the medium)
- velocity in vaccum is highest and the velocity in medium must be slowest.
45
When light travel through medium of one refractive index from one another
- one get diffracted
- other get refracted bends at interface between two medium
- N1= air, N2 =water
- which of the velocity is higher?
- water has higher refractive index so the light bends and perpendicular towards medium of higher refractive index N2>N1 meaning light is travelling faster in N1.
- Light bends toward normal of medium of higher refractive index light is travelling faster in N2 > 1.
- angle of incidence is higher than angle of refraction
On other hand, if N1 (air) angle of incidence is higher than angle of refraction N2 ( water) N1>N2, it means that the angle of refraction is higher than angle of incidence. Light travels faster in N2
- refraction follows mathematical relationship known as law of refraction or snell’s law
N1 sin theta1= N2 sin theta 2
46
Refraction follow mathematical relationship known as law of refraction
-meaning that angle of incidence is dependent upon refractive index through medium
- if angle of incidence is zero, this means light travels as refractive radiation going from higher refractive index to lower.
- as angle of incidence increases, angle of refractive increase through medium.
47
Three magnification - case ( rules on how light travels in biconvex lens
1. Ray passing through lens parallel to its axis passes through the focal points F of the lens on the other side
- refracted, and converge through the focal length
2. A ray passing through the centre of either converging/diverging lens do not change direction
- no deviation and no mage produce
3. A ray passing through converging lens through its focal point exits parallel to its axis.
- get refracted and emerging rays is now parallel to its axis
Note: image are proved where all the three rays intersept
48
Magnification case 1
- di= distance from lens and image
- do = distance from object and lens
- f = focal length
- hi= length/height from the lens and image
- ho = height/ length from the object and image
Magnification =M
M = (hi/ho = di/do)
Focal length = 1/f = 1/do =>1/di
49
Magnification case 2
- opposite of case 1, everything moves to other side of the object without any object being produced.
- it converged at focus and also refracted no deviation and image formed
- image is upright in the top of the object virtual, intersection is not real, deceived intersection
50
Continuation on magnification
- if image goes beyond 2x ( eg 4-5) of the focal length the image is inverted but they are smaller in size of object
- if object is placed exactly 2x lens, it produces image of exact same size
- as image is placed close to the focus, then we start getting a magnification
51
Compound microscope
- uses two biconvex lenses
- objective lens: placed closer to objects produced magnification on the other side of length
- eye pieces or occular : sight objects
- inverted image produced initially formed within focal length of the second lens producing magnified upright image. I.e magnification produced form compound microscopes is Mtotal = Mo x occular eye
52
Polarization
- transmission of light
- when light is polarized parallel to two polarized filter, the intensity of light remain same. We have max brightness
- when light is perpendicular to the polarized filter light, the intensity of light transmitted is total darkness/ extinctions max darkness( block light) so no light
- intensity of light Ii = density of light ( Ii cos theta)
53
Filter
- allows original light to pass through easily
- caused vibration direction
- plane polarized light confine to angle of plane
- improves properties of light
54
Lecture 6
55
Plane polarized light
- uses lower polarizer , vibration in one plane direction
- things are better observed in ppl
56
Optical properties are best viewed in ppl
- opacity: appear black on ppl
- grain size : description of what we see, diff variations in size. Crystal formation: euhedral( perfect faces developed), subhedral ( rounded) but same general characteristics), Anhedral ( shows irregular shapes)
- color
- relief
57
Refractive index
- measures of how light travel, minerals that travel will bend
- it’s problematic but we will use relief instaef
58
Relief
- how well we can see the crystals and the boundary of a mineral grains stand out relative to its surroundings crystals mounting
- depends on diff Refractive index
- if minerals and surrounding has diff r.i light diverge away from edge. Refraction ( bend light).
59
Relief
- high relief ; when minerals have high refractive index than its surroundings crystals mounting medium. Difference in r.i
- low relief: if the diff is similar, like surrounding medium and minerals are same or less then its low or negative relief
60
How to determine relief
- garnet has high relief and r.l
- micas has moderate
- calcite R.I orientation changes when rotate ie light travels in velocity of the minerals orientation
- we use properties of becke line
- becky line appear outside the edge is positive relief. Minerals refractive index higher than medium
Becke lines moves in the direction of higher refractive index
- if it moves from outside to inward then we have high relief convergence
- if moves from inward to outside then it’s negative low relief meaning that minerals os lower than medium surrounding. It diffracted
