Address 14 (11/13/2006) Expository Mineralogy Section 1: Nature of Light Prologue to Optical Mineralogy.

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Nature of Light. Unmistakable light is a type of electromagnetic radiation, which can be portrayed as heartbeats or influxes of electrical energyTravels in straight lines with a transverse wave movement. Unpolarized light. Energized light. Qualities of Light. Wavelength (?) - separation between wave crests; measured in angstroms (
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Address 14 (11/13/2006) Analytical Mineralogy Part 1: Nature of Light Introduction to Optical Mineralogy

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Nature of Light Visible light is a type of electromagnetic radiation , which can be described as heartbeats or floods of electrical vitality Travels in straight lines with a transverse wave movement Unpolarized light Polarized light

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Attributes of Light Wavelength ( ) - separation between wave crests; measured in angstroms (Å); characterizes shade of unmistakable light Amplitude ( A ) - tallness of light waves; compares to the power/brilliance of light Frequency () - number of light waves passing an altered point for each second; measured in cycles/second Velocity ( v = ·  ) ; rate of light in a vacuum = 3·10 18 Å/sec = c e.g. for orange light in a vacuum,  = 6000 Å,  = 5·10 14/sec Light backs off as it goes through denser substances. Since the recurrence of light never shows signs of change as it goes through various substances, an abatement in light speed mirrors a relative decline in its wavelength.

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Electromagnetic Spectrum From Bloss, 1961

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Reflection and Refraction of Light When light goes from a low thickness medium (e.g. air) into a higher thickness non-obscure medium (e.g. a mineral), part will be reflected and part will be go through, however be twisted and moderated – refracted. Point of reflection (  r\' ) approaches the occurrence edge (  i ) Angle of refraction (  r ) will vary from the episode edge contingent upon the adjustment in speed between the two substances

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Refractive Index and Snell\'s Law Index of Refraction – n substance = c/v substance >1 light speed in air ≈ c , so n air ~ 1 Snell\'s Law-predicts the edge of refraction at the interface of two substances with various refractive indicies: n i sin  i = n r sin  r  r = sin - 1 (n i/n r x sin  i )

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Critical Angle of Refraction Critical occurrence edge  i is the place  r > 90 º ; i.e. all out reflection  i basic = sin - 1 (n r/n i x sin 90 º ); e.g., for n i = 2, n r = 1;  i basic = 30 º for n i = 1.5, n r = 1;  i basic = 41.8 º

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Successive Refraction

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Refraction, Relief, and the Becke Line Relief is how much an eliminate remains from its environment and is a declaration of the differentiation in record of refraction dull diagram

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Becke Line Test From Bloss (1961)

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Dispersion Because n is identified with light speed, which is identified with wavelength ( v = ·  ) , distinctive wavelengths of light will have diverse refraction indicies inside a specific substance Illuminating a mineral with white light may in this manner lead to shading scattering

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Polarization of Light radiating from a point source vibrates every which way typical to the spread course Light can be enraptured (made to vibrate in one plane) by particular retention (OR) or by reflectance (OL)

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Anisotropy Indicies of refraction can fluctuate in all minerals (aside from those in the isometric framework) contingent upon the introduction of light beam. Such minerals are said to be anisotropic . Isometric minerals, glass, fluids and gasses have a solitary refraction record esteem paying little heed to the introduction of light beams. Such substances are said to be isotropic .

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Next Lecture 11/15/06 Optical Properties of Uniaxial Minerals Read: Klein p. 298-303 Perkins and Henke, p. 14-22

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