ERTH 2102 Lecture Notes - Lecture 99: Enstatite, Liquidus, Birefringence
15 Dec 2015
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Document Summary
Most minerals differ in terms of their hardness. Albite, orthoclase, mircocline, sanidine are alkali feldspars. The energy difference between d- (or f-) orbitals of transition elements corresponds to a specific wavelength of visible light. Discrete wavelengths of visible light are absorbed when valance electrons of transition elements jump into a state of higher potential energy. Absorption of red and infrared light due to cu2+ [copper] elbaite (tourmaline) appears blue. Idiochromatic: self coloured due to their major element composition, their colour is constant and predictable. Candle light is poor in blue wavelengths, so sapphire becomes black. Refractive index, n = velocity of light in vacuum / velocity of light in mineral. Dispersion: change of optical properties (e. g. , n) with wavelength. The optical indicatrix an imaginary 3-d surface with axial lengths proportional to n. After entering a crystal, light is split into two rays (n and n) Michel-l vy chart shows the relationships between , and t.
