The result, we see blue as the yellow and some greens are removed from the visible spectrum. As they do they absorb energy, the same wavelength as yellow light from the photons. Light entering the sapphire excites the valence electrons causing them to jump/pass through the trap. In simple terms, Fe and Ti cause small kinks or traps in the atomic structure of corundum that affects the valence electrons of the surrounding aluminum atoms. Fe and Ti actually play with valence electrons in the crystal to cause a “colour trap” us to see blue. I emphasize the use of interaction here as the iron and titanium don’t just replace aluminum in the crystal structure like chromium. Unlike ruby where it gets its colour from traces of chromium within the crystal structure, sapphire blue colour comes from the interaction of iron (Fe) and titanium (Ti) with aluminum in the crystal structure. Now for the fun part, how is sapphire blue? This is an interesting question as sapphires change the game a little when it comes to colouring. (Note, habit is how the mineral crystallizes)
1) Trigonal Crystal System, not to be confused with crystal habit.Unless a colour is in front of the word “sapphire” then it is assumed one is referring to the blue variety of corundum. Confusing, I know, even to a gemmologist.
All other colours are classified as “fancy sapphire”, this is odd as the beryl varieties had unique names but when it comes to corundum in the yellow, violet or green hues then they are referred to as a “ yellow sapphire”, “ green sapphire” and “ violet sapphire”. Sapphire is the blue variety and padparadscha is the pink/orange variety. Now just to clarify this before we continue, as I stated in the blog about rubies, corundum is naturally colourless, and thus colour comes from impurities within the stone. Sapphires, the bluest of the blue gemstones, are more than just blue. While October is the better of the two, the birthstone for September is better, in my biased opinion. The colour, cool nights, no bugs, scarfs, sweaters, crunching leaves and the smell pumpkin spice coffee in the air. I mean every season has its perks, this summer especially was wonderful with the heat, but fall still is the best. September, the beginning of the BEST season, autumn.
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