1_ Introduction to Optical Mineralogy, Light & Theories-converted.pdf

introduction to optical minerology and description about optical properties of mineral and importance and uses of optical minerology and how to identify a mineral through its optical properties.

1. Optical
Mineralogy
(GEOL. 405)
Department of Geology
University of Malakand

2. Optical Mineralogy
Course Contents
➢Introduction
•Mineral -definition and specification
•Mineralogy and its division
•Scope and purpose of optical mineralogy
➢Optical classification of minerals
•Determinative optical properties of minerals
•Properties in plane polarized light
•Relief & Relative refractive index
•Colour, Pleochroism and Absorption
•Properties in crossed Nicols/light
•Extinction and its types
•Determination of extinction angle
•Elongation and its types
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3. Optical Mineralogy…
➢InterferenceFigures
•Uniaxialinterferencefigures
•Opticaxis-centeredfigure
•Off-centeredfigure&Flashfigure
•Biaxialinterferencefigures
•Acutebisectrix-centeredfigure
•Opticaxis-centered&Off-centeredfigure
•Determinationofopticsign
•Uniaxial&Biaxialminerals
•OpticalIndicatrices
•Isotropicindicatrix
•AnisotropicIndicatrices
•Uniaxial&BiaxialIndicatrices
•Opticaxialangle(2V)
•DispersionandcrystallographicorientationofX,YandZ
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4. LabWork
•Thepolarizingmicroscope
•Determinationoftheopticalpropertiesofminerals
•Reliefandrelativerefractiveindex
•Colour,Pleochroismandabsorption
•Patternofcleavagetraces(ifany)
•Interferencecolour,Twinning(ifany)
•Typesofextinction&extinctionangle
•Signofelongation(determinationofslow/fastraydirectionsinminerals)
•Interferencefigures,Determinationofopticsign
•Recognitionofsomeofthecommonmineralswiththehelpoftheiropticalproperties
•Determinationoftheplagioclasecomposition(anorthitecontent)withthehelpofextinctionangle
Optical Mineralogy…
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5. RecommendedBooks
•PrinciplesofMineralogybyWilliam.H.B.,1990,OxfordUniversityPress.
•MineralogybyPerkins,D.,2002,PrenticeHall.
•OpticalMineralogybyKerr,P.F.,1959,McGrawHill.
•MineralsandRocksbyKlein,C.,1989,JohnWiley&Sons.
•MineralsinThinSectionsbyPerkins,D.,2000,PrenticeHall.
•IntroductiontoOpticalMineralogybyNesse,W.D.,2003,OxfordUniversityPress.
•AnAtlasofMineralsinThinSectionbySchulze,D.J.,2003,CD-RM,Oxford
•Dana,S.E.andFord,W.E.,1962.ATextbookofMineralogy.JohnWiley&sons,NewYork.
•Hurlbut,C.S.,Jr.,1971.Dana’sManualofMineralogy.JohnWiley&sons,NewYork.
•Berry,L.G.andMason,B.,1959.Mineralogy.Freeman,SanFrancisco.
Optical Mineralogy…
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6. Grading Criteria
6
ITEM
MAXIMUM MARKS FOR
COURSES WITH LABORATORY
(2+1 CH)
Mid Term Examination 15%
Internal Marks (Assignments, Quizzes, Presentations)20%
Laboratory 15%
Final Term Examination 50%
TOTAL 100%

7. Introduction to Optical Mineralogy
•Itisdefinedas“abranchofmineralogyinwhichwestudytheoptical
propertiesofamineral/rock”.
•Opticalpropertiesarethose“whichdependsonlight”.
•Opticalmineralogyexaminestheinteractionoflightwithvisiblelight.
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8. Electromagnetic spectrum& visible portion
Violet (400 nm) →Red (700 nm)
White = ROYGBV
(can be separated by dispersion)
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9. Branches of Mineralogy
•Mineralogy:Studyofminerals.Itcanbestudiedinmanyways.
•PhysicalMineralogy:Physicalpropertiese.g.coloretc.
•ChemicalMineralogy:Chemicalcompositionofminerals.
•Crystallography:Crystalaspect/structureofminerals.
•OpticalMineralogy:Opticalpropertiesofminerals.
•DescriptiveMineralogy:Alloftheabovepropertiesarestudied.
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10. Why Optical Mineralogy?
•Therearesomemineralswhicharenotrecognizablebyother
properties,sotodifferentiateandidentifythosemineral,theiroptical
propertiesarestudied.
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11. Mineral
•A mineral is a substance which is :
•Naturally occurring
•Inorganic origin
•Solid state
•Definite chemical composition
•Regular internal structure
e.g. feldspar, olivine etc.
•Sometime mineral is composed of only one element like Diamond and
silver etc.
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12. Mineral…
•Plagioclaseisoneofthefeldspargroups.AllPlagioclaseareAlumino-silicateof
Na&Ca.
•Na–AlSilicate
•Ca–AlSilicate
•Insomecases:100–90%Na–AlSilicate
000–10%Ca–AlSilicate
•ItiscalledAlbite.
•IfamountofNa–AlSilicatedecreasese.g.90–70%Na–AlSilicate
10–30%Ca–AlSilicate
•ThenitiscalledOligoclase.
•Allthemineralsarecrystallinesubstances.
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13. •Facesaretheexternalmanifestationofregularinternalstructure.
•Mineralscan’tbeamorphous.Somemineralshavecrystalline
structureatthetimeofformationbutwiththetimetheylosetheir
regularstructure.e.g.Allanite,itcontainradioactiveelements.
•Someamorphoussolidbecomecrystallinewiththetime.
•Mineraloids–Naturallyoccurringamorphoussolids.e.g.Opaletc.
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Mineral…

14. Light
•Lightisdefinedas“aradiantenergywhichisemitted,propagatedandtransmitted
intheformofrays”.
•Theradiantenergyconsistsofthevisiblepartofelectromagneticspectrum.
•Ƴ–rays
•X–rays Wavelength(ʎ)
•UV–rays increases
•Light
•Infraredrays
•Radiowaves
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15. Light…
•Ƴ–rays,X–rays&UVrayshavetooshortʎthatwecan’tseeit.Ontheother
handradiowavesandinfraredrayshavelargeʎthereforewecan’tseeittoo.
•Lightisvisibletousbecauseithasʎ=3700A
o
–7800A
o
.
•Sevencolorsbecauseof7differentranges.
VIBGYOR
•Violet,Indigo,Blue,Green,Yellow,Orange,Red
•3700A
o
7800A
o
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16. 16
SpectrumofEMradiation

17. 17
Spectrum of EM radiation

18. •Theyaredifferentfromoneanotherbutwhytheyaregrouptogether.
•Theansweristhattheyhavesomecommoncharacteristics.
•Allofthemtravelinstraightlines
•Allofthemtravelwiththesamespeedinvaccum.e.g.300,000km/second
or299,792,458meters/second.
•Allofthemundergoreflectionandrefraction.
•Allofthemundergograting.
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Light…

19. •Visiblelightispolychromatic(severalcolors).Ifallthesecolorsstrikeour
eyes,thecolorinterpretedbybrainiswhite.Forroutinework(optical
measurement)weneedwhitelighte.g.sunlight,tungstenlamporlight
fromwindow.
•Butforgreateraccuracyweneedmonochromaticlight.
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Light…

20. •Mono–single,chromatic–light
•Monochromaticlightdoesn’tmeanthatithavenecessarilysame
wavelength.Butthevariationwillbeuptorestrictedrange.Normally
weusesodiumlightwhensodiumvapourlampisused.
•ʎ=5890–5896A
0
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Light…

21. Theories About Propagation of Light
➢CorpuscularTheory
•Accordingtothistheorylightistransmittedascorpuscles.
➢QuantumTheory
•Accordingtothistheorylightistransmittedintheformenergy
packetscalledquantas.
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22. ➢ElectromagneticTheory
•Accordingtothistheorylighttravelintheformofwavesanditgottwo
vectors.Oneiselectricinnatureandtheotherismagneticinnature.They
vibrateperpendiculartooneanother.Sothepropagationoflightisalso
perpendicular.
➢DualNatureofLight
•Accordingtothistheorylightistransmittedandpropagatedintheformof
corpusclesandwaves,respectively. 22
Theories About Propagation of Light…

23. Refractive Index ORIndex of Refraction
•Itisaquantitywhichtellstheamountofrefractionwhenthelightpassing
fromoneregiontoanother. OR
•Itistheratioofthevelocityoflightinvacuum(C)tothevelocityoflightina
givenmedium(C
m).
n=C/C
m
OR
•Itisthenumericalexpressionofopticaldensity.
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24. •Opticaldensity–Theamountofresistancewhichamaterialofferstothe
passageoflight.
•ThereisadirectrelationshipbetweendensityandR.I.
•CisalwaysmorethanC
mbecausevelocityoflightismaximuminvacuum.
•Velocitydependsupontheresistanceofferbyanymaterialmedium.
•nwillalwaysbeanumberanditshouldbemorethanone.
e.g.n
air=1.0003
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Refractive Index ORIndex of Refraction…

25. Types of Media
•Mediafromwhichlightpasseswillbeoftwotypes.
•Isotropicmedia
•Anisotropicmedia
➢IsotropicMedia
•Theyarestructurallyhomogeneousinwhichconstituentatoms,ionsorparticlesare
uniformlydistributed.
•Theanglebetweenthevibrationdirectionoflightandlineoftransmissionwillbe90
o
.
•e.g.Cubicsolids.
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26. ➢AnisotropicMedia
•Theyarestructurallyinhomogeneous.
•Theatomicpackinginonedirectionisdifferentfromtheotherdirection.
•Thevibrationdirectionmaydeviatefromtheperpendicularitybutnot
necessarily.
•e.g.allmineralswhicharenon-cubicandthereforetheycanhavedifferent
R.Iindifferentdirection.
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Types of Media…

27. Isotropic Vs Anisotropic…
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28. Thanks
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