ORE DEP (ORE MICROSCOPY) Flashcards
Thin section: Petrography = _________: Ore Micrsocopy
Polished Sections
Difference of Ore Microscope vs Petrographic Microscope?
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
The distance between the specimen and the objectives
Free working Distance
Types of Objectives
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
The degree by which the image is enlarges as light passes through the objective
Magnification of an object
Measure of the ability to distinguish fine structureal details in a specimen and determines the depth of focus and the useful range of magnification
Numerical Aperture (NA)
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
Dry/Air Lenses
Thickness of the cover glass in Thin Sections
0.17-0.18 mm
Commonly used objectives for reflected light microscopy especially when high magnification and high resln is required
Immersion objectives
Immersion Oil Index of refraction
n=1.515
The higher the objective power
The higher the FWD, the larger tha angular apertures
Difference of Oculars in Petrog in ore microscopy
Do not have crosshairs!!
color of filter to produce daylight illumniation
Pale Blue
Field Diapgrahm vs Aperture Diapgrahm
Aperture D. - reduce stray scattered liht
Field D. - controls the angle of cone of light incident
Most Critical Component of a Ore Microscope
Reflector
Types of Reflectors
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
Used to control or provide a specified wavelength
Monochromators
Used to measure Reflectance
Photometers
Used to measure grain size
Stage Micrometers
Process in which chemical solutions are used to enhance structures within grains subected for mineral identification
Chemical Etching
Commong Ecthants
HNO3 -Nitric Acid
Ammonium Dichromate - HCl Soln
H2SO4 - Sulfuric Acid
Advance Technique in Ore Microscopy
EPMA
Fluid Inclusion
SEM
Stable Isotope Study
XRD
Set-up for Observing Color in Reflected Light
?Illuminator Field Diapgrahm and Illimunator Apertur Diapgrahm opened wide
?Low Power Objective
?High Voltage for light of good intensity
?Polarizer in, Analyzer out
The amount of light reflected back
Reflectance
Reflectance formula (R%)
(Intensity of Reflected Light / Intensity of Incident Light ) x 100%
Factors which can affect amount of light reflected back to the observer
?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
Change of Reflectance
Bireflectance (Anisotopism)
Change of color or tint
Reflection Pleochroism
Reflections within semi-translucent to transparent minerlas
Internal Reflection
Minerals which does not exhibit Bireflectance and Reflection Pleochroism
(Parang Birefringence and Pleochroism sa Petrg)
Isotropic Minerals (Cubic Minerals)
Basal Sections of Hexaonal and Tetragonal Cyrstals
Bireflectance is the measure of
The difference between the maximum and minimum values of reflectance percentage
The resistance of particular mineral to abrasion during polishing process
Polishing Hardness
The property in which hard minerals may stand slightly above the surfaces of softer grains in the section
Polishing Relief (Relief is a function of Hardness)
The relative amount of surface scratchin an the depth of scratches that cross grain
Scratch Hardness
Line test that is used in Reflected Ore microscopy which makes use of scratches
Kalb Line Test
Mohs Scale of Hardness for ore minreals
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
Seen in polished sections as one or more sets of parallel cracks
Cleavage
How are three cleavage direction seen under reflected light especially seen in Galena, Magnetite and Pentlandite?
Parallel rows of triangular pits
Three types of twinnig obersved in Ore Microscopy
1) Growth
2) Inversion
3) Deformation
What may be the caused of Zonal Sturctures in ore minerals
1) Depositional Pause during Growth
2) Different Growth Rates w/ or w/o inclusions
3) Chemcial Variations during growth
Strong Bireflectance
Graphite
Molyb
Covellite
Stibnite
Vallerite
Moderated
Marcasite
hematite
Niccolite
Cubanite
Pyrrhotite
Weak
Ilmenite
Arsenopyrite
