NATS 1870 Lecture Notes - Lecture 17: Electronic Band Structure, Fluorine, Lapis Lazuli
28 Sep 2016
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Document Summary
Colour in minerals and gemstones: minerals: naturally occurring solid. Processes orderly, internal structure: atoms are arranged in a definite pattern. Typically found when rock or magma cool: rocks clusters or mixtures of minerals, gemstones a type of mineral. When cut + polished form a gemstone with brilliance, luster e. g. sapphire, ruby, emerald, amethyst, diamond. Processes that give rise to colour in minerals and gemstones: transition metal compound: Mineral contains a transition metal in its crystal structure. Energy level spacing of transition metal easily absorbs visible wavelengths: gives that mineral its colour. The mineral always has that specific colour (no colour variations) Impurity will give colour variations depending on which impurity allochromatic . Corundum very common base, to which impurities can be added: creates various gemstones. If ~19o chromium added cr+++ (chromium ion) replace the aluminum ion in the corundum: cr transition metal: its outer e- readily absorbs short wavelengths. Some impurity can create different colours, depending on base".
