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GLE 2024 (Day 3) > ORE DEP (ORE MICROSCOPY) > Flashcards

ORE DEP (ORE MICROSCOPY) Flashcards

1
Q

Thin section: Petrography = _________: Ore Micrsocopy

A

Polished Sections

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2
Q

Difference of Ore Microscope vs Petrographic Microscope?

A

Ore Microscope uses Incident Light which allows examination of PLOSHED SURFACES of OPAQUE MINERALS under REFLECTED LIGHT

Light source above the thin section

Petrographic: Transmitted Light
Light source below the section

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3
Q

The distance between the specimen and the objectives

A

Free working Distance

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4
Q

Types of Objectives

A

1) Achromat - corrected for spherical aberration of 1 color (Yl.Grn) and for Chromatic Abberation for two colors
2) Apochromat - corrected for spherical aberrationof 2 colors (blue green) and Chromatic Abberation for primary colors
3) Flourite - Between

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5
Q

The degree by which the image is enlarges as light passes through the objective

A

Magnification of an object

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6
Q

Measure of the ability to distinguish fine structureal details in a specimen and determines the depth of focus and the useful range of magnification

A

Numerical Aperture (NA)

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7
Q

Most commonly used low-to medium- magnification objetives fo ore microscopic work and is designed to have only air in between the ibjective and the sample

A

Dry/Air Lenses

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8
Q

Thickness of the cover glass in Thin Sections

A

0.17-0.18 mm

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9
Q

Commonly used objectives for reflected light microscopy especially when high magnification and high resln is required

A

Immersion objectives

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10
Q

Immersion Oil Index of refraction

A

n=1.515

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11
Q

The higher the objective power

A

The higher the FWD, the larger tha angular apertures

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12
Q

Difference of Oculars in Petrog in ore microscopy

A

Do not have crosshairs!!

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13
Q

color of filter to produce daylight illumniation

A

Pale Blue

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14
Q

Field Diapgrahm vs Aperture Diapgrahm

A

Aperture D. - reduce stray scattered liht
Field D. - controls the angle of cone of light incident

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15
Q

Most Critical Component of a Ore Microscope

A

Reflector

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16
Q

Types of Reflectors

A

1) 45 plane glass reflector - some is reflected some light lost
2) Smith Reflector - light enters at an angle of 22.5 deg and isotropic samples appears uniformly black in XPL
3) Totally relecting Prism - light is reflected downward through 0.5 aperture of the objective and is reflected back upward through the other half

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17
Q

Used to control or provide a specified wavelength

A

Monochromators

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18
Q

Used to measure Reflectance

A

Photometers

19
Q

Used to measure grain size

A

Stage Micrometers

20
Q

Process in which chemical solutions are used to enhance structures within grains subected for mineral identification

A

Chemical Etching

21
Q

Commong Ecthants

A

HNO3 -Nitric Acid
Ammonium Dichromate - HCl Soln
H2SO4 - Sulfuric Acid

22
Q

Advance Technique in Ore Microscopy

A

EPMA
Fluid Inclusion
SEM
Stable Isotope Study
XRD

23
Q

Set-up for Observing Color in Reflected Light

A

?Illuminator Field Diapgrahm and Illimunator Apertur Diapgrahm opened wide
?Low Power Objective
?High Voltage for light of good intensity
?Polarizer in, Analyzer out

24
Q

The amount of light reflected back

A

Reflectance

25
Q

Reflectance formula (R%)

A

(Intensity of Reflected Light / Intensity of Incident Light ) x 100%

26
Q

Factors which can affect amount of light reflected back to the observer

A

?Cyrstallographic Orientation of the Polished Surface
relative to the vibration directions of linearly polarized incident light
?Wavelength of light
?Angle of Incidence
?Defree of Polish

27
Q

Change of Reflectance

A

Bireflectance (Anisotopism)

28
Q

Change of color or tint

A

Reflection Pleochroism

29
Q

Reflections within semi-translucent to transparent minerlas

A

Internal Reflection

30
Q

Minerals which does not exhibit Bireflectance and Reflection Pleochroism
(Parang Birefringence and Pleochroism sa Petrg)

A

Isotropic Minerals (Cubic Minerals)
Basal Sections of Hexaonal and Tetragonal Cyrstals

31
Q

Bireflectance is the measure of

A

The difference between the maximum and minimum values of reflectance percentage

32
Q

The resistance of particular mineral to abrasion during polishing process

A

Polishing Hardness

33
Q

The property in which hard minerals may stand slightly above the surfaces of softer grains in the section

A

Polishing Relief (Relief is a function of Hardness)

34
Q

The relative amount of surface scratchin an the depth of scratches that cross grain

A

Scratch Hardness

35
Q

Line test that is used in Reflected Ore microscopy which makes use of scratches

A

Kalb Line Test

36
Q

Mohs Scale of Hardness for ore minreals

A

Argentite 2-2.5
Galena 2.5
Chalcopyrite 3.5-4
tetraherite 3-4.5
Niccolite 5-5.5
Magnetite 6
Ilmenite 5.5-6

37
Q

Seen in polished sections as one or more sets of parallel cracks

A

Cleavage

38
Q

How are three cleavage direction seen under reflected light especially seen in Galena, Magnetite and Pentlandite?

A

Parallel rows of triangular pits

39
Q

Three types of twinnig obersved in Ore Microscopy

A

1) Growth
2) Inversion
3) Deformation

40
Q

What may be the caused of Zonal Sturctures in ore minerals

A

1) Depositional Pause during Growth
2) Different Growth Rates w/ or w/o inclusions
3) Chemcial Variations during growth

41
Q

Strong Bireflectance

A

Graphite
Molyb
Covellite
Stibnite
Vallerite

42
Q

Moderated

A

Marcasite
hematite
Niccolite
Cubanite
Pyrrhotite

43
Q

Weak

A

Ilmenite
Arsenopyrite

GLE 2024 (Day 3) (48 decks)

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