How smell works is one of those things we’re chipping away at, but we just don’t have it worked out yet. There is a prevailing theory. There are also some less popular but still intriguing newcomers being put forth by…intriguing newcomers. A predictive theory of smell eludes us - given a structure, we can make some guesses as to how it’s going to smell, but they’re pretty crude: sulfur stinks. Gee, thanks. It’s not quite that bad, but close.
Olfaction is also unique because a Nobel was issued for working out how every other sense works, long before that for smell. Richard Axel and Linda Buck’s smell Nobel was for working out the genes encoding odor receptors. A predictive theory of the relationship between chemical structure and odor remains elusive. Until we get it figured out, we will have plenty of weirdoes in the odorant world. After we get it figured out, well, they’ll still be weirdoes, but at least we’ll understand them and be able to relate to their stinky plight. One such rascal is indole.
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Corundum is a funny one. It is aluminum (III) oxide, or Al₂O₃. This means that it is composed of aluminum atoms, three electrons shy of the zero oxidation state (the shiny, silvery, regular metal). You could also call this an Al³⁺ compound, instead of an aluminum (III) compound. The charge is balanced by the oxygen (-2) atoms. In a crystal, it looks like this:

The funny thing about corundum is, when you have it in a clean single crystal, you get something much different. You know them as sapphires…

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