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- 1. Optical Mineralogy (GEOL. 405) Department ofGeology 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 2
- 3. Optical Mineralogy… ➢ InterferenceFigures • Uniaxial interference figures • Optic axis-centered figure • Off-centered figure & Flash figure • Biaxial interference figures • Acute bisectrix-centered figure • Optic axis-centered & Off-centered figure • Determination of optic sign • Uniaxial & Biaxial minerals • Optical Indicatrices • Isotropic indicatrix • Anisotropic Indicatrices • Uniaxial & Biaxial Indicatrices • Optic axial angle (2V) • Dispersion and crystallographic orientation of X, Y and Z 3
- 4. Lab Work • Thepolarizing microscope • Determination of the optical properties of minerals • Relief and relative refractive index • Colour, Pleochroism and absorption • Pattern of cleavage traces (if any) • Interference colour, Twinning (if any) • Types of extinction & extinction angle • Sign of elongation (determination of slow/fast ray directions in minerals) • Interference figures, Determination of optic sign • Recognition of some of the common minerals with the help of their optical properties • Determination of the plagioclase composition (anorthite content) with the help of extinction angle Optical Mineralogy… 4
- 5. Recommended Books • Principlesof Mineralogy by William. H.B., 1990, Oxford University Press. • Mineralogy by Perkins, D., 2002, Prentice Hall. • Optical Mineralogy by Kerr, P.F., 1959, McGraw Hill. • Minerals and Rocks by Klein, C., 1989, John Wiley & Sons. • Minerals in Thin Sections by Perkins, D., 2000, Prentice Hall. • Introduction to Optical Mineralogy by Nesse, W.D., 2003, Oxford University Press. • An Atlas of Minerals in Thin Section by Schulze, D.J., 2003, CD-RM, Oxford • Dana, S. E. and Ford, W. E., 1962. A Textbook of Mineralogy. John Wiley & sons, New York. • Hurlbut, C. S., Jr., 1971. Dana’s Manual of Mineralogy. John Wiley & sons, New York. • Berry, L. G. and Mason, B., 1959. Mineralogy. Freeman, San Francisco. Optical Mineralogy… 5
- 6. Grading Criteria 6 ITEM MAXIMUM MARKSFOR 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 OpticalMineralogy • It is defined as “a branch of mineralogy in which we study the optical properties of a mineral / rock”. • Optical properties are those “which depends on light”. • Optical mineralogy examines the interaction of light with visible light. 7
- 8. Electromagnetic spectrum &visible portion Violet (400 nm) → Red (700 nm) White = ROYGBV (can be separated by dispersion) 8
- 9. Branches of Mineralogy •Mineralogy: Study of minerals. It can be studied in many ways. • Physical Mineralogy: Physical properties e.g. color etc. • Chemical Mineralogy: Chemical composition of minerals. • Crystallography: Crystal aspect / structure of minerals. • Optical Mineralogy: Optical properties of minerals. • Descriptive Mineralogy: All of the above properties are studied. 9
- 10. Why Optical Mineralogy? •There are some minerals which are not recognizable by other properties, so to differentiate and identify those mineral, their optical properties are studied. 10
- 11. Mineral • A mineralis 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. 11
- 12. Mineral… • Plagioclase isone of the feldspar groups. All Plagioclase are Alumino-silicate of Na & Ca. • Na – Al Silicate • Ca – Al Silicate • In some cases: 100 – 90 % Na – Al Silicate 000 – 10 % Ca – Al Silicate • It is called Albite. • If amount of Na – Al Silicate decreases e.g. 90 – 70 % Na – Al Silicate 10 – 30 % Ca – Al Silicate • Then it is called Oligoclase. • All the minerals are crystalline substances. 12
- 13. • Faces arethe external manifestation of regular internal structure. • Minerals can’t be amorphous. Some minerals have crystalline structure at the time of formation but with the time they lose their regular structure. e.g. Allanite, it contain radioactive elements. • Some amorphous solid become crystalline with the time. • Mineraloids – Naturally occurring amorphous solids. e.g. Opal etc. 13 Mineral…
- 14. Light • Light isdefined as “a radiant energy which is emitted, propagated and transmitted in the form of rays”. • The radiant energy consists of the visible part of electromagnetic spectrum. • Ƴ – rays • X – rays Wavelength (ʎ) • UV – rays increases • Light • Infrared rays • Radio waves 14
- 15. Light… • Ƴ –rays, X – rays & UV rays have too short ʎ that we can’t see it. On the other hand radio waves and infrared rays have large ʎ therefore we can’t see it too. • Light is visible to us because it has ʎ = 3700 Ao – 7800 Ao. • Seven colors because of 7 different ranges. V I B G Y O R • Violet, Indigo, Blue, Green, Yellow, Orange, Red • 3700 Ao 7800 Ao 15
- 16. 16 Spectrum of EMradiation
- 17. 17 Spectrum of EMradiation
- 18. • They aredifferent from one another but why they are group together. • The answer is that they have some common characteristics. • All of them travel in straight lines • All of them travel with the same speed in vaccum. e.g. 300,000 km / second or 299,792,458 meters / second. • All of them undergo reflection and refraction. • All of them undergo grating. 18 Light…
- 19. • Visible lightis polychromatic (several colors). If all these colors strike our eyes, the color interpreted by brain is white. For routine work (optical measurement) we need white light e.g. sunlight, tungsten lamp or light from window. • But for greater accuracy we need monochromatic light. 19 Light…
- 20. • Mono –single, chromatic – light • Monochromatic light doesn’t mean that it have necessarily same wavelength. But the variation will be up to restricted range. Normally we use sodium light when sodium vapour lamp is used. • ʎ = 5890 – 5896 A0 20 Light…
- 21. Theories About Propagationof Light ➢ Corpuscular Theory • According to this theory light is transmitted as corpuscles. ➢ Quantum Theory • According to this theory light is transmitted in the form energy packets called quantas. 21
- 22. ➢ Electromagnetic Theory •According to this theory light travel in the form of waves and it got two vectors. One is electric in nature and the other is magnetic in nature. They vibrate perpendicular to one another. So the propagation of light is also perpendicular. ➢ Dual Nature of Light • According to this theory light is transmitted and propagated in the form of corpuscles and waves, respectively. 22 Theories About Propagation of Light…
- 23. Refractive Index ORIndex of Refraction • It is a quantity which tells the amount of refraction when the light passing from one region to another. OR • It is the ratio of the velocity of light in vacuum (C) to the velocity of light in a given medium (Cm). n = C / Cm OR • It is the numerical expression of optical density. 23
- 24. • Optical density– The amount of resistance which a material offers to the passage of light. • There is a direct relationship between density and R.I. • C is always more than Cm because velocity of light is maximum in vacuum. • Velocity depends upon the resistance offer by any material medium. • n will always be a number and it should be more than one. e.g. nair = 1.0003 24 Refractive Index OR Index of Refraction…
- 25. Types of Media •Media from which light passes will be of two types. • Isotropic media • Anisotropic media ➢ Isotropic Media • They are structurally homogeneous in which constituent atoms, ions or particles are uniformly distributed. • The angle between the vibration direction of light and line of transmission will be 90o. • e.g. Cubic solids. 25
- 26. ➢ Anisotropic Media •They are structurally inhomogeneous. • The atomic packing in one direction is different from the other direction. • The vibration direction may deviate from the perpendicularity but not necessarily. • e.g. all minerals which are non-cubic and therefore they can have different R.I in different direction. 26 Types of Media…
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